![myself. This source he identifies with God, but, as far as the
argument goes, it might equally well have been found, as by Locke,
in the original constitution of matter; all that the argument requires is
that it shall be placed in something outside the succession of
presentations themselves. On the other hand, he also argues that
since the existence of the physical world means simply the fact of its
being presented to consciousness, when its contents cease to be
present to my consciousness they must be present to that of God.
And here again the objection might be suggested, that if presence to
my own experience, while it lasts, is an adequate account of the
esse of a thing, it does not appear why I should recognise the reality
of any other experience. If I am to hold that disappearance from my
experience does not destroy the reality of anything, I must logically
also hold that its being, while I perceive it, is not exhausted by my
awareness of it. Its esse cannot be merely percipi.
The complete solution of Berkeley’s difficulty would be premature
at this point of our discussion. But we may at once point out its
principal source. It arises from his failure to take adequate account of
the purposive aspect of experience. Experience, as we have seen, is
not mere awareness of a succession of presented objects, it is
awareness of a succession determined by a controlling interest or
purpose. The order of my experiences is not something simply given
me from without, it is controlled and determined by subjective
interest from within. Berkeley, in fact, omits selective attention from
his psychological estimate of the contents of the human mind. He
forgets that it is the interests for which I take note of facts that in the
main determine which facts I shall take note of, an oversight which is
the more remarkable, since he expressly lays stress on “activity” as
the distinguishing property of “spirits.”[41]
When we make good the
omission by emphasising the teleological aspect of experience, we
see at once that the radical disparity between the relation of the
supreme and the subordinate mind to the world of facts disappears. I
do not simply receive my presented facts passively in an order
determined for me from without by the supreme mind; in virtue of my
power of selective attention, on a limited scale, and very imperfectly,
I recreate the order of their succession for myself.](https://image.slidesharecdn.com/129465-241214192054-16b4150f/85/Download-Complete-Streaming-Data-Pipelines-with-Kafka-MEAP-Stefan-Sprenger-PDF-for-All-Chapters-21-320.jpg)
![Again, recognition of the teleological aspect of all experience goes
far to remove the dissatisfaction which we may reasonably feel with
the other half of Berkeley’s argument. When I conceive of the “facts”
of experience as merely objects presented to my apprehension,
there seems no sufficient reason for holding that they exist except as
so presented. But the moment I think of the succession of presented
facts as itself determined by the subjective interests expressed in
selective attention, the case becomes different. The very expression
“selective attention” itself carries with it a reminder that the facts
which respond to my interests are but a selection out of a larger
whole. And my practical experience of the way in which my own
most clearly defined and conscious purposes depend for their
fulfilment upon connection with the interests and purposes of a wider
social whole possessed of an organic unity, should help me to
understand how the totality of interests and purposes determining
the selective attention of different percipients can form, as we have
held that it must, the harmonious and systematic unity of the
absolute experience. The fuller working out of this line of thought
must be left for later chapters, but it is hardly too much to say that
the teleological character which experience possesses in virtue of its
unity with feeling is the key to the idealistic interpretation of the
universe.[42]
Idealism, i.e. the doctrine that all reality is mental, as we shall have
repeated opportunities of learning, becomes unintelligible when
mental life is conceived of as a mere awareness of “given”
presentations.
§ 7. We may now, before attempting to carry out in detail our
general view of what is involved in being real, enumerate one or two
philosophical doctrines about the nature of real existence which our
conclusion as to the connection of reality with experience justifies us
in setting aside. And, first of all, we can at once see that our previous
result, if sound, proves fatal to all forms of what is commonly known
as Realism. By Realism is meant the doctrine that the fundamental
character of that which really is, as distinguished from that which is
only imagined to be, is to be found in its independence of all relation
to the experience of a subject. What exists at all, the realist holds,
exists equally whether it is experienced or not. Neither the fact of its](https://image.slidesharecdn.com/129465-241214192054-16b4150f/85/Download-Complete-Streaming-Data-Pipelines-with-Kafka-MEAP-Stefan-Sprenger-PDF-for-All-Chapters-22-320.jpg)
![Being consists in its not depending for its existence or its character
on relation to an experience. The differences of detail as to the
number and nature of independent “reals,” though of great
importance for our complete estimate of an individual realist’s
philosophical position, do not affect our general verdict on the
tenability of the first principle of Realism.
The one point of divergence among realists which may be
considered as of more than secondary importance for our present
purpose, is the difference between what we may call Agnostic and
Dogmatic Realism. Agnostic Realism, while asserting the ultimate
dependence of our experience upon a reality which exists
independently of experience, denies that we can have any
knowledge of the nature of this independent reality. The independent
reality by which all experience is conditioned is, on this view, an
Unknowable or Thing-in-itself,[43]
of which we are only logically
entitled to say that it certainly is, but that we do not in the least know
what it is. The doctrine of Agnostic Realism has probably never been
carried out by any thinker with rigid consistency, but it forms a
leading feature of the philosophy of Kant as expounded in his First
Critique, and through Kant has passed into English thought as the
foundation of the systems of Sir William Hamilton and Mr. Herbert
Spencer.[44]
Dogmatic Realism, of which Leibnitz and, at a later date, Herbart
are the most important representatives in modern philosophy, on the
contrary, while maintaining that real being is independent of
experience, at the same time holds that it is possible to have positive
knowledge not only of its existence but of its nature. In principle, both
these forms of Realism have been already excluded by the argument
of Book I. chap. 2, § 4. The supreme importance of the principle on
which the argument rests may perhaps warrant us in once more
briefly recurring to it. Our reasoning, it will be remembered, took the
form of a challenge. Produce any instance you please, we said to the
realist, whom we had not then learned to know by that name, of what
you personally regard as reality, and we will undertake to show that it
derives its reality for you from the very fact that it is not ultimately
separable from the experience of a subject. A thing is real for you,
and not merely imaginary, precisely because in some aspect of its](https://image.slidesharecdn.com/129465-241214192054-16b4150f/85/Download-Complete-Streaming-Data-Pipelines-with-Kafka-MEAP-Stefan-Sprenger-PDF-for-All-Chapters-24-320.jpg)
![than as that of which no mind is ever aware, of which no purpose
has ever to take account as a condition of its fulfilment? But to think
of it thus is to attribute to it, as its definition, precisely that
independence in which the realist finds the mark of ultimate reality.
And if “independence” constitutes unreality, presence to and union
with experience must be what constitutes reality.
Yet, however fatal this line of argument may be to the principle of
the realistic contention, we ought not to be satisfied with such a mere
general refutation. We must try to see what is the element of truth in
the realistic views to which they owe the plausibility they have
always possessed for minds of a certain type. In Philosophy we are
never really rid of an error until we have learned how it arises and
what modicum of truth it contains.
(1) Agnostic Realism. We may begin with Agnosticism, with which
we ought now to have no serious difficulty. Agnostic Realism, as we
have seen, is in principle a doubly self-contradictory theory. For it
combines in one breath the irreconcilable declarations that the reality
of things is unknowable and that it knows it to be so.[45]
Further, as
we have just said, it makes alleged contradictions which only exist in
and for experience, its sole ground for affirming that something, of
which we can only specify that it is outside all experience,
transcends cognition. To have grasped these two points is to have
disposed of Agnosticism as a metaphysical theory.
Yet with all its defects Agnosticism still enshrines one piece of truth
which the metaphysician is peculiarly prone to forget. Of all men the
metaphysician, just because his special interest is to know
something final and certain about Reality, is the most apt to
exaggerate the amount of his certain knowledge. It is well to be
reminded that the certainty with which we may say that Reality is
experience is compatible with a very imperfect and limited theoretical
insight into experience itself. In actual life this is a far from unfamiliar
fact; the literature of common sense is full of observations to the
effect that we never really know our own hearts, that the most
difficult task of the sage is to understand himself, and so forth,—
complaints which all turn on the point that even our own limited direct
experience of our own meanings and purposes goes far beyond
what we can at any moment express in the form of reflective](https://image.slidesharecdn.com/129465-241214192054-16b4150f/85/Download-Complete-Streaming-Data-Pipelines-with-Kafka-MEAP-Stefan-Sprenger-PDF-for-All-Chapters-26-320.jpg)
![knowledge. Yet it is easy, when we come to deal in Metaphysics with
the nature of ultimate Reality, to forget this, and to suppose that the
certainty with which we can say that the ultimately Real is an
experience justifies us in wholesale dogmatising about the special
character of that experience. As a protest against such exaggerated
estimates of the extent of our theoretical knowledge of the nature of
Reality, Agnosticism thus contains a germ of genuine and important
truth, and arises from a justifiable reaction against the undue
emphasising of the merely intellectual side of our experience, of
which we have already seen, and shall hereafter still more fully see,
ground to complain as a besetting weakness of the metaphysically
minded.
(2) Dogmatic Realism, that is, Realism with admittedly knowable
independent “reals,” is a much more workable doctrine, and in one of
its forms, that of the so-called “naïve realism” which supposes the
world of experienced things with all its perceived qualities to exist
independently of any relation to an experiencing subject in precisely
the same form in which we experience it, fairly represents the
ordinary views of unphilosophical “common-sense” men. Nothing
seems more obvious to “common sense” than that my perception of
a thing does not bring it out of nothing into existence, and again does
not create for it new qualities which it had not before. It is because
the thing is already there, and has already such and such a nature,
says “common sense,” that I perceive it as I do. Therefore the whole
world of perceived things must exist independently in the same form
in which they are perceived, as a condition of my perception of them.
When this view comes to be worked out as a philosophical theory,
it usually undergoes some transformation. The fact of illusion, and
the experimentally ascertained subjective differences between
individual percipients,[46]
or between different states of the same
percipient, make it hard for the realist who wishes to be scientific to
maintain that all the perceived qualities of experienced things are
equally independent of the experiencing subject. Reflection usually
substitutes for the “naïve” realism of everyday life, a theory of
“scientific” realism according to which the existence and some of the
known properties of the experienced world are independent of the
experiencing subject, while others are regarded as mere secondary](https://image.slidesharecdn.com/129465-241214192054-16b4150f/85/Download-Complete-Streaming-Data-Pipelines-with-Kafka-MEAP-Stefan-Sprenger-PDF-for-All-Chapters-27-320.jpg)
![effects arising from the action of an independent reality on the
subject’s consciousness. With the further differences between the
various types of scientific realism, according to the special properties
which are held to belong to things independently of the percipient
subject, we are not at present concerned.[47]
It is, of course, clear that our general argument against the
existence of any reality except as in an experience tells just as much
against “naïve” realism and its more reflective outgrowth “scientific”
realism as against Agnosticism. But the very plausibility and wide
diffusion of realistic views of this type make it all the more necessary
to reinforce our contention by showing what the truth Realism
contains is, and just where it diverges from truth into fallacy. Nor is it
specially difficult to do this. The important elements of truth
contained in Realism seem to be in the main two. (i) It is certain that
a thing may be real without being consciously present as a
distinguishable aspect in my experience. Things do not begin to exist
when I begin to be aware of them, or cease to exist when I cease to
be aware of them. And again, the fact that I make mistakes and am
subject to illusion shows that the qualities of things are not
necessarily in reality what I take them to be. (2) Further, as is shown
by the fact of my imperfect understanding of my own feelings and
purposes, something may actually be an integral part of my own life
as an experiencing subject without my clearly and consciously
recognising it as such when I reflect on the contents of my
experience.
But precisely how much do these two considerations prove? All
that is established by the first is the point on which we have already
insisted, that it is not my experience which constitutes Reality; and
all that is established by the second, that experience, as we have
already repeatedly seen, is not merely cognitive. But the admission
of both these positions brings us not one step nearer the conclusion
which the realist draws from them, that real existence is independent
of all experience. Because it is easy to show that the reality of a
thing does not depend on its being explicitly recognised by any one
finite percipient or any aggregate of finite percipients, and again, that
there is more in any experience of finite percipients than those
percipients know, the realist thinks he may infer that there are](https://image.slidesharecdn.com/129465-241214192054-16b4150f/85/Download-Complete-Streaming-Data-Pipelines-with-Kafka-MEAP-Stefan-Sprenger-PDF-for-All-Chapters-28-320.jpg)
![general scheme of purposes and interests expressed in our system
of railway traffic, and it is precisely this connection, with a scheme of
purposes and interests, which makes the runaway train a reality and
not a mere fiction of an ingenious philosopher’s imagination. If Mr.
Hobhouse’s argument proves the independent reality of the train in
the tunnel, it ought equally to prove, and does equally prove, the
independent existence of Selkirk’s fluctuations from hope to despair
and back again on his isolated rock. And precisely because it proves
both conclusions equally, the sort of independence it establishes
cannot be independence of experience. Like all realist arguments, it
turns on the identification of experience with the cognitive aspect of
experience, an identification too often suggested by the language of
the “idealists” themselves.[48]
§ 8. The persistent vitality of Realism is due to its protest against
the fallacies of an opposing theory which has of late especially found
favour with some distinguished students of natural science, and
which we may conveniently call Subjectivism.[49]
Realism, as we saw,
started from the true premisses, that there are real facts of which my
experience does not make me explicitly aware, and that my cognition
even of my own experience is incomplete, and argued to the false
conclusion that there are therefore realities independent of any
experience. Subjectivism reasons in the opposite way. It asserts truly
that there is no reality outside experience, and then falsely
concludes that I can know of no reality except my own cognitive
states. Its favourite formula are expressions such as, “We know only
the modifications of our own consciousness,” “All we know is our
own perceptions,” “Nothing exists but states of consciousness.”
These formulæ are not all obviously identical in meaning, but the
exponents of Subjectivism seem to use them without any conscious
distinction, and we shall probably do the theory no injustice if we
criticise it on the assumption that the expressions are meant to be of
identical signification.
Now it is clear that the logical consequences of the subjectivist
doctrine are so subversive of all the practical assumptions upon
which daily life is based, that they should require the most stringent
proof before we give our assent to them. If Subjectivism is true, it
follows immediately that not merely the “whole choir of heaven and](https://image.slidesharecdn.com/129465-241214192054-16b4150f/85/Download-Complete-Streaming-Data-Pipelines-with-Kafka-MEAP-Stefan-Sprenger-PDF-for-All-Chapters-30-320.jpg)
![furniture of earth,” but the whole of humanity, so far as I have any
knowledge of its existence, is a mere subjective affection of my own
“consciousness,” or, as the scientific subjectivist usually, for some
not very obvious reason, prefers to say, of my own brain. Every
argument which the subjectivist can produce to show that “things”
are, for my knowledge at any rate, “modifications of my own
consciousness,” applies to the case of my fellow-men with as much
force as to the case of the inorganic world. The logical inference
from the subjectivist’s premisses, an inference which he is rarely or
never willing to draw, would be that he is himself the sole real being
in a world of phantoms, not one of which can with any certainty be
said to correspond to a real object. And conversely, any valid ground
for recognising the existence of my fellow-men as more than “states
of my own consciousness,” must equally afford ground for admitting
the reality, in the same general sense, of the rest of the world of
things familiar to us from the experiences of everyday life.[50]
For if
any one of the things composing the world of practical life has a
reality which is not dependent upon its presence to my particular
experience, then there is the same reason for believing that every
other such thing has a like reality, unless there happen to be special
grounds for regarding the perception to which it is present as an
hallucination.
We must not, however, simply dismiss the subjectivist theory in
this summary way. We must examine the doctrine in detail
sufficiently to discover where the fallacy comes in, how it arises, and
what modicum of sound philosophic insight it may possibly contain.
To take these three points in logical order—
(a) The current arguments for Subjectivism are often so stated as
to confuse together two quite distinct positions. When it is said that
what we perceive is “our own subjective states,” the meaning
intended may be either that there is, at least so far as I am able to
know, no real existence in the universe except that of my “states of
consciousness”; or again, that there are such realities, but that the
properties which I perceive do not belong to them in their own nature
but are only subjective effects of their action upon my
“consciousness,” or, if you prefer to speak in physiological language
upon my nervous system. Now, many of the arguments commonly](https://image.slidesharecdn.com/129465-241214192054-16b4150f/85/Download-Complete-Streaming-Data-Pipelines-with-Kafka-MEAP-Stefan-Sprenger-PDF-for-All-Chapters-31-320.jpg)
![the one thing of which no one, except the introspective psychologist,
is ever aware is his own perceptive state in the act of perceiving, and
that, even in the case of the psychologist who sets himself purposely
to study his own states, no perceptive state ever perceives itself.
What I am aware of when I look at a red surface is not “myself-as-
perceiving-red,” but the splash of red colour itself. When I see a
man, I do not perceive “myself-as-seeing-a-man,” but I perceive the
other man. So when I take a resolution to act in a certain way or
realise that I am in a certain mood, what I am directly aware of is not
“myself-as-forming-the-resolution” or “myself-as-in-the-mood,” but
the resolution or the mood. Even when, as an introspective
psychologist, I sit down to study the formation of resolutions or the
peculiarities of emotional moods by reflection on my own experience,
the state in which I study the formation of a resolution or the nature
of a mood is not itself the state of resolving or of experiencing the
mood in question. We cannot too strongly insist that, if by “self-
consciousness” is meant a cognitive state which is its own object,
there is no such thing, and it is a psychological impossibility that
there should be any such thing, as self-consciousness. No cognitive
state ever has itself for its own object. Every cognitive state has for
its object something other than itself.[51]
Even where I make an assertion about my subjective condition, as
when I say “I know I am very angry,” the state of knowing about my
feeling is as distinct from the feeling itself as the state of knowing
that I see red is from the red colour that I see. What the subjectivist
does is to confuse the two. Because the act of knowing is itself a
state of the knowing subject, and because in some cases the
knowledge may again have reference to some other state of the
same subject, he infers that what I know at any moment is my own
subjective condition in the act of knowing. In other and more
technical words, he confuses the cognitive act or state with its own
object. To what absurd results this confusion would lead him, if he
were logical in the inferences he makes from it, we have already
seen. We can now see that psychologically the confusion is a double
one. (1) The subjectivist confuses experience with mere awareness
of a presented content. He ignores the presence of the true
“subjective” factor of selective attention throughout experience, and](https://image.slidesharecdn.com/129465-241214192054-16b4150f/85/Download-Complete-Streaming-Data-Pipelines-with-Kafka-MEAP-Stefan-Sprenger-PDF-for-All-Chapters-34-320.jpg)
![is thus led to forget that all experiences imply an element which is in
the experiencing mind but not presented to it. (2) And in confining his
attention to the presentational aspect of experience, he goes on to
confound the presented content with the fact of its presentation. As
against this second confusion it is essential to a true theory of
knowledge to emphasise three points of distinction between the
presented content or object of a cognitive state and the state itself,
considered as a process in the history of an experiencing subject. (1)
The cognitive state is never its own object, it refers to or cognises an
object distinct from its own existence as a psychical occurrence. This
is the truth which Realism distorts into the doctrine that the object of
knowledge must have a reality of “independent of” experience. (2)
The object of knowledge is never created by the occurrence of the
psychical state in which a particular percipient becomes aware of its
existence. This is just as true of so-called “merely ideal” objects as of
physical things. The properties of the natural logarithms or of the
circular functions in trigonometry are just as independent of my
knowledge of them as the qualities of the trees and animals I should
see if I turned from my writing desk and looked out at the window. (3)
The object of knowledge has always a character of which only a
fragment is ever presented to my perception or reflection in any
cognitive state. Every cognitive state refers to or stands for a great
deal more than it directly means to me.
(3) The origin of the subjectivist fallacy, as has been brilliantly
shown by Avenarius,[52]
is to be found in the “intrasubjective
intercourse” of a plurality of percipients capable of communicating
their experience to each other. So long as I am dealing solely with
myself as an experiencing being and my relation to my own
environment, there is no possibility of a subjectivist interpretation. In
my own direct experience I have to do neither with “mental states”
nor with mere “objects of cognition,” but with things which in various
ways by their interference assist or hinder the accomplishment of my
various purposes, and of which I have therefore to take note, so as
to adapt my ways of reaching my ends to their ways of behaviour.
Hence the “natural” view of the world, for a single experiencing
being, would be that of “naïve realism,” to which the things forming
my environment are real in precisely the same sense in which I am](https://image.slidesharecdn.com/129465-241214192054-16b4150f/85/Download-Complete-Streaming-Data-Pipelines-with-Kafka-MEAP-Stefan-Sprenger-PDF-for-All-Chapters-35-320.jpg)
![experience there is an underlying substratum of genuine philosophic
truth. For, as we have more than once insisted, there is manifestly a
great deal more in my own experience than what is at any time
present as the object of conscious cognition. Or, as Mr. Bradley is
fond of putting it, there is always more in my mind than before it. I
am never fully aware at any moment even of the full nature of my
own purposes and feelings. This is why the deceitfulness of my own
heart has become a common-place of religious self-examination as
well as of worldly wisdom.
Again, every increase of insight into our own real feelings and
purposes involves increased insight into the feelings and purposes of
the other feeling beings with whom we stand in the various relations
of social intercourse.[53]
Hence it might fairly be contended that fully
to know your own meaning, fully to understand what you want, would
imply complete insight into the structure of the whole world of reality,
—in fact, that self-knowledge and knowledge of the universe must
ultimately be the same thing. The systematic unity of the whole world
of experience may be so complete that there is nothing in it
anywhere which does not correspond to some element in the
experience of every one of its members. Each member may, like the
monads of Leibnitz, represent the whole system though at very
different levels of coherency and from very different points of view.
But such a conception, though it would concede to Subjectivism that
whatever forms a part of the system of real being somehow falls
within my individual experience, would take as the foundation of its
assertion that very distinction between what is implicitly present in
my experience and what is explicitly before it which Subjectivism
consistently ignores. Whether the doctrine as thus re-stated can be
affirmed as more than a fascinating possibility, we shall be better
able to judge when we have discussed in our next chapter the
systematic unity of Reality.
Consult further:—F. H. Bradley, Appearance and Reality, chaps.
13, 14; T. Case, Physical Realism, pt. 1; L. T. Hobhouse, The Theory
of Knowledge, pt. 3, chap. 3, The Conception of External Reality; H.
Lotze, Metaphysic, bk. i. chap. 7 (pp. 207-231 of vol. i. in Eng.
trans.); J. S. Mackenzie, Outlines of Metaphysics, bk. i. chap. 3,](https://image.slidesharecdn.com/129465-241214192054-16b4150f/85/Download-Complete-Streaming-Data-Pipelines-with-Kafka-MEAP-Stefan-Sprenger-PDF-for-All-Chapters-37-320.jpg)
![however, might suggest biological conceptions of growth,
dependence on an external environment, etc., which would be out of
place. But the student may compare with what has been said of the
“purposive” character of individuality Spinoza’s conception of the
being of a thing as a conatus in suo esse perseverandi.
39. For a full examination of the relation between reality and
scientific symbolism, consult Ward, Naturalism and Agnosticism, part
1. The more clearly it is realised that scientific hypotheses are
essentially a system of mathematical symbolism, the more
impossible it becomes to suppose that they deal directly with the
concrete nature of things.
40. In Principles of Human Knowledge, §§ 70-75, Berkeley indeed
seems on the very verge of denying that God Himself “perceives” the
“ideas” which by His action He excites in us. But at § 139 we find
that a “spirit” means “that which perceives ideas, and wills and
reasons about them,” and in the third Dialogue it is expressly stated
that sensible things are “perceived by God” [Works, Edit. in Bohn’s
Libraries, vol. i. p. 368]. In fact, from the psychological standpoint of
Berkeleian sensationalism, to deny God’s possession of “ideas” (i.e.
sense-contents) would have been tantamount to denying His
spirituality.
41. Unfortunately Berkeley, like so many philosophers, thought of
“activity” as primarily an external relation between a “cause” and the
material on which it “works.” This is probably why he failed to realise
the “active” character of the perceptual process.
42. The reader will do well to compare with the whole of the
foregoing section the treatment of perception as essentially
teleological in Dr. Stout’s Manual of Psychology,3
bk. iii. pt. 1, chap.
2.
I need hardly observe that recognition of the fundamental
significance of purpose and selection for mental life does not of itself
entail the adoption of “voluntarist” views in Psychology. What is
fundamental for real mental life may perfectly well admit of analysis
into hypothetical simpler elements for the purpose of the
psychologist. Thus the admission that all mental life is teleological
and selective need not involve the adoption of such metaphysical
theories of activity as are adversely criticised by Mr. Bradley in his](https://image.slidesharecdn.com/129465-241214192054-16b4150f/85/Download-Complete-Streaming-Data-Pipelines-with-Kafka-MEAP-Stefan-Sprenger-PDF-for-All-Chapters-40-320.jpg)
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- 7. Streaming Data Pipelines with Kafka 1. Welcome 2. 1_Getting_into_data_streaming 3. 2_A_walk_through_Kafka_and_its_ecosystem 4. 3_Integrating_data_systems_in_real-time_with_Kafka_Connect
- 8. Welcome Thank you for purchasing Streaming Data Pipelines with Kafka in MEAP. We are used to getting groceries delivered in under ten minutes and we can access almost any information at any time via search engines, yet most data integrations are implemented with batch pipelines that leave data systems out of sync at most times. Streaming data pipelines are a modern alternative to batch pipelines: They replicate data between data systems like database systems and APIs in real-time and can process them on the way. As a foundational technology of modern, real- time data architectures, streaming data pipelines enable downstream data consumers to always work with fresh data. Unfortunately, you still need to become an expert in many technologies to successfully apply them. I am writing this book for data engineers, software developers, and others who face use cases for data- integration at their workplace. It aims to provide a complete introduction to the concepts, development, and deployment of streaming data pipelines, with a strong focus on the open-source technology Apache Kafka, the de-facto industry standard for event streaming. The book not only teaches foundational concepts of streaming data pipelines but prepares the reader to successfully implement them at their workplace. Throughout the book, we will help an imaginary e-commerce company to migrate its legacy batch pipelines to a modern streaming architecture and overcome the typical challenges of such migrations. My goal is to develop the best book possible. Your feedback on early versions of the book is essential for its development and is highly appreciated. Please don’t hesitate to post your questions, comments, or suggestions in the liveBook discussion forum. -Stefan Sprenger In this book
- 9. Welcome 1 Getting into data streaming 2 A walk through Kafka and its ecosystem 3 Integrating data systems in real-time with Kafka Connect
- 10. 1 Getting into data streaming This chapter covers An introduction to streaming data pipelines and their building blocks The shortcomings of traditional batch data pipelines The relationship between data streaming and batch processing Use cases for stream processing In the last decades, software has eaten the world. Across all industries, companies have adopted software solutions at their core to unlock new business models, improve their efficiency, and provide more value to customers. Businesses use CRM tools to manage customer relationships, drive their decision-making with reporting and dashboards, and predict the impact of price changes with AI models. Similar to cars requiring fuel to drive, these software systems run on data. Modern businesses employ a plethora of different software solutions that they cannot operate as isolated silos but need to integrate with each other to derive the maximum value. Integrating software systems has never been an easy task but is becoming even more complex these days. We are used to getting groceries delivered in ten minutes and can access almost any information at any time via search engines - Why are most data integrations neither working in real-time nor syncing data changes instantly after their occurrence? At the same time, businesses operate an ever-growing number of different systems and easily spend six to seven digits on cloud computing per year, making them favor efficient data integrations that sync only relevant data changes instead of performing resource-wasting bulk loads. Fortunately, there is a modern, event-driven approach to cope with the demanding requirements of data-driven businesses: Streaming data pipelines. 1.1 Introducing streaming data pipelines
- 11. Data pipelines integrate different data systems. They replicate data from data sources, like database systems, to data sinks, like data warehouses, and can process the data on the way. Most datasets are unbounded. Whether it is a transactional database system empowering an online shop, a cloud object store holding sales data, or an API exposing user data; it is very likely that these datasets are not static but experience changes frequently. To this end, most data pipelines are not one- off deployments but must be recurringly or continuously executed. 1.1.1 Going one step back: Batch data pipelines Traditionally, data pipelines are implemented with batch processing: They recurringly extract all data from data sources, processing them in one go, and publish the processed data to data sinks. Figure 1.1 shows a batch data pipeline that integrates MySQL, a transactional database system, with ClickHouse, a data warehouse. Each night at 2 AM, the batch pipeline (1) extracts all data from MySQL, (2) cleans up the data, and (3) ingests the processed data into ClickHouse. While batch pipelines are fairly straightforward to implement, they put a tremendous load on all components of the architecture, which precludes a frequent execution. As a consequence, data consumers, like dashboards, reporting tools, or analytical applications, do not have access to up-to-date data. Figure 1.1 Each night at 2 AM, a batch data pipeline replicates data from MySQL to ClickHouse and processes them on the way.
- 12. Note While most database systems provide the same interface, the Structured Query Language (SQL), they typically do not optimize for all kinds of workloads but focus on either transactional, write-heavy operations or analytical, ready-heavy use cases. For instance, MySQL is a solid choice for managing the continuously-changing state of an application, like an online shop, but does not cater well to the analytical queries executed by dashboards, reporting tools, and data-intensive applications.
- 13. The simple and straightforward implementation of batch data pipelines comes at the cost of several drawbacks in the timely, efficient, and robust processing of data: 1. Batch data pipelines cannot be executed with a high frequency. Business teams cannot support decisions with current information but are almost always working with outdated data, which might lead to missed business opportunities. 2. Batch pipelines are quite heavy and put a lot of load onto data source systems because they extract all data at each execution. To avoid impacting the performance of data sources, batch pipelines are typically executed outside of business hours. Debugging production issues is a challenge and rollouts of bug fixes must wait until the next execution. 3. Single runs of batch pipelines can easily take multiple hours because they are processing very large datasets. If batch pipelines fail while executing, they might leave data sinks in a corrupted state until the next execution of the pipeline. It might also happen that pipelines finish their execution after the start of the business day. 4. Batch pipelines see data sources at the time of data extraction and might miss incremental updates that occurred in between two runs. 1.1.2 Building blocks of streaming data pipelines Similar to batch pipelines, streaming data pipelines replicate data from data sources to data sinks and can process them on the way. The big difference is that they are being executed continuously, work in real-time, and process incremental updates. Once a change has been applied to a data source, streaming data pipelines extract the change event (basically a row-level INSERT, UPDATE, or DELETE event), process it, and publish the processed change event to the data sink. Figure 1.2 Employing a streaming data pipeline to replicate data from MySQL to ClickHouse in real-time and process them on the way.
- 14. Figure 1.2 illustrates how the example from the prior section could be implemented with a streaming data pipeline: Connectors integrate the streaming data pipeline with external data sources and external data sinks, here MySQL and ClickHouse. The data source connector employs change data capture (CDC) for extracting row-level data change events from the replication log of MySQL in real- time. The data sink connector publishes processed change events to ClickHouse. Connectors may apply lightweight data transformations to events after extracting them from a data source or before publishing
- 15. them to a data sink, e.g., for converting between data formats. The open-source community provides a few projects that implement connectors for data streaming use cases; the most popular and complete one is Kafka Connect, which is part of the official Apache Kafka release. Kafka Connect provides hundreds of different connectors for integrating Apache Kafka with external data systems, like MySQL or ClickHouse. While using existing connectors helps you to save time and minimize potential errors, developing custom connectors can make sense if you are dealing with uncommon data systems that are not (yet) covered by Kafka Connect. Stream processors handle the processing of events while replicating them from data sources to data sinks. They often integrate with an event store, like Apache Kafka. Stateless stream processing operations, such as transformations or filters, process event by event and do not consider the order or time of the events. Stateful stream processing operations, such as aggregations or joins, perform computations over windows of events. They are more complex than stateless operations, require maintaining and persisting the state of the computations, and need a notion of time. They also need mechanisms for dealing with scenarios, like the late arrival of events. Traditionally, stream processors are implemented with projects, such as Kafka Streams or Apache Flink, and in programming languages, like Java, Scala, or Python. Recently, a lot of tools started introducing SQL layers on top of their programmatic APIs, which simplifies the development of stream processing logic at the cost of flexibility. If you are heavily building on top of Apache Kafka, Kafka Streams might be a reasonable choice. Event stores, like Apache Kafka, persist events in a reliable and scalable way. Streaming data pipelines employ event brokers to persist (1) events that have been extracted by source connectors from an external data source, like MySQL, and are passed to the stream processor and (2) events that have been processed by the stream processor and are consumed by the sink connector for publishing them to an external data sink, like ClickHouse. Using dedicated storage for events instead of passing them directly between the connectors and the stream processor is very useful for a number of reasons, like the mitigation of backpressure, which occurs when consumers cannot keep
- 16. up with the pace of the producers, or the replaying of events. Event stores also enable streaming data pipelines to achieve a high tolerance towards failures and temporary outages of single components. Apache Kafka is the most popular storage solution in the industry. Even most of its competitors, like Azure Event Hubs or RedPanda, provide a Kafka- compatible API. Apache Kafka provides low-level interfaces for consuming and producing events; Kafka Connect and Kafka Streams build on top of these interfaces and may help you save time when implementing connectors or stream processing logic. 1.1.3 Integrating data in real-time with Apache Kafka Let us have a closer look at how you can use Apache Kafka, Kafka Connect, and Kafka Streams to build a data pipeline that streams order data from an online shop to a data warehouse in real-time. Figure 1.3 Visualization of a streaming data pipeline capturing CDC events from a MySQL database with Kafka Connect, processing them with Kafka Streams, and inserting them into ClickHouse with Kafka Connect; Kafka topics are used for persisting records.
- 17. When a website visitor places an order on the website of an e-commerce shop, the shop software executes an INSERT statement for adding a new row to the table orders of the underlying database system, here MySQL. Most database systems offer log files for replicating data between multiple database instances; one database instance can subscribe to the log file of another database instance and consume all data change events in real-time, allowing different database instances to stay in sync. The great thing about replication logs is that subscribing to them does not put any load onto the database system, because it bypasses the database system’s query layer and lets subscribers directly access the log file. MySQL’s replication log is called
- 18. the Binary Log. The open-source project Debezium, which provides Kafka Connect source connectors for various database systems, leverages this mechanism for detecting and capturing changes in real-time and without impacting the performance of MySQL. Once MySQL has flushed the change event to its Binary Log, Debezium extracts the event and produces it to an Apache Kafka topic, here called orders_raw. Internally, Debezium maintains the latest position of the Binary Log that it has successfully processed and persists that information in another Kafka topic, which allows resuming data extraction after restarts or downtimes without reprocessing data. The Kafka Streams application subscribes to the Kafka topic orders_raw, consumes new records immediately after their occurrence, and applies a custom data masking function to the records for masking credit card numbers. After processing the records, the Kafka Streams application produces them to another Kafka topic, called orders_clean. The Kafka Streams application is a regular Java application. A Kafka Connect sink connector subscribes to the Kafka topic orders_clean, consumes new records immediately after their occurrence, and publishes them to ClickHouse by executing INSERT statements. The Kafka Connect connectors and the Kafka Streams application are loosely coupled, share data via Kafka topics, and are deployed independently of each other. That is, restarting the Kafka Streams application does not affect the uptime of the connectors and vice versa. 1.1.4 Benefits and challenges of streaming data pipelines Streaming data pipelines represent a much more natural, robust, and efficient approach to dealing with unbounded datasets than their batch-based counterparts. Instead of performing recurring bulk loads at fixed times, streaming data pipelines continuously replicate data change events from the consumed data sources to the downstream data sinks. Notably, streaming data pipelines offer the following benefits:
- 19. Data sinks are always in sync with data sources: Streaming data pipelines minimize the gap between the time a change event occurs in the data source and the time the processed event arrives at the data sink, often offering sub-second latencies. They allow downstream data consumers, regardless of whether these are humans manually interpreting the data or applications processing the data in a programmatic manner, to work with up-to-date data. Capturing of all changes occurring in data sources: Log-based CDC connectors make all changes from a data source available to streaming data pipelines and downstream data consumers, while batch pipelines observe the state of the data source at the time of data extraction. Having access to high-fidelity data is beneficial for a number of use cases, including audit logs. Better resource footprint: When employing CDC, streaming data pipelines must process only the data that have changed, i.e., incremental changes. They keep all other data untouched and help to reduce the load on all involved systems and improve the overall usage of computing resources, which potentially leads to a reduction in cost. Minimal impact on production database systems: Processing incremental changes instead of performing bulk loads is beneficial for reducing the load on the consumed data source, because much less data is touched at execution time. When employing log-based CDC, streaming data pipelines further reduce the load on the consumed database system because they do not need to execute SELECT * FROM queries but can extract data from the replication log files of the database system. Predictable workload patterns: Batch pipelines show peak resource consumption at execution time and are stale for the rest of the time, which wastes a lot of compute resources. Streaming data pipelines have rather flat workload patterns as they continuously replicate change events. They reduce the cost and allow for the usage of elastic workload scaling, as available in cloud computing technologies like Kubernetes. There is no free lunch. While providing clear benefits and advantages over batch processing, the architectures of streaming systems are more complex and require expertise in multiple technologies. This book helps you to overcome the hurdles associated with data streaming and prepares you for the
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- 21. myself. This source he identifies with God, but, as far as the argument goes, it might equally well have been found, as by Locke, in the original constitution of matter; all that the argument requires is that it shall be placed in something outside the succession of presentations themselves. On the other hand, he also argues that since the existence of the physical world means simply the fact of its being presented to consciousness, when its contents cease to be present to my consciousness they must be present to that of God. And here again the objection might be suggested, that if presence to my own experience, while it lasts, is an adequate account of the esse of a thing, it does not appear why I should recognise the reality of any other experience. If I am to hold that disappearance from my experience does not destroy the reality of anything, I must logically also hold that its being, while I perceive it, is not exhausted by my awareness of it. Its esse cannot be merely percipi. The complete solution of Berkeley’s difficulty would be premature at this point of our discussion. But we may at once point out its principal source. It arises from his failure to take adequate account of the purposive aspect of experience. Experience, as we have seen, is not mere awareness of a succession of presented objects, it is awareness of a succession determined by a controlling interest or purpose. The order of my experiences is not something simply given me from without, it is controlled and determined by subjective interest from within. Berkeley, in fact, omits selective attention from his psychological estimate of the contents of the human mind. He forgets that it is the interests for which I take note of facts that in the main determine which facts I shall take note of, an oversight which is the more remarkable, since he expressly lays stress on “activity” as the distinguishing property of “spirits.”[41] When we make good the omission by emphasising the teleological aspect of experience, we see at once that the radical disparity between the relation of the supreme and the subordinate mind to the world of facts disappears. I do not simply receive my presented facts passively in an order determined for me from without by the supreme mind; in virtue of my power of selective attention, on a limited scale, and very imperfectly, I recreate the order of their succession for myself.
- 22. Again, recognition of the teleological aspect of all experience goes far to remove the dissatisfaction which we may reasonably feel with the other half of Berkeley’s argument. When I conceive of the “facts” of experience as merely objects presented to my apprehension, there seems no sufficient reason for holding that they exist except as so presented. But the moment I think of the succession of presented facts as itself determined by the subjective interests expressed in selective attention, the case becomes different. The very expression “selective attention” itself carries with it a reminder that the facts which respond to my interests are but a selection out of a larger whole. And my practical experience of the way in which my own most clearly defined and conscious purposes depend for their fulfilment upon connection with the interests and purposes of a wider social whole possessed of an organic unity, should help me to understand how the totality of interests and purposes determining the selective attention of different percipients can form, as we have held that it must, the harmonious and systematic unity of the absolute experience. The fuller working out of this line of thought must be left for later chapters, but it is hardly too much to say that the teleological character which experience possesses in virtue of its unity with feeling is the key to the idealistic interpretation of the universe.[42] Idealism, i.e. the doctrine that all reality is mental, as we shall have repeated opportunities of learning, becomes unintelligible when mental life is conceived of as a mere awareness of “given” presentations. § 7. We may now, before attempting to carry out in detail our general view of what is involved in being real, enumerate one or two philosophical doctrines about the nature of real existence which our conclusion as to the connection of reality with experience justifies us in setting aside. And, first of all, we can at once see that our previous result, if sound, proves fatal to all forms of what is commonly known as Realism. By Realism is meant the doctrine that the fundamental character of that which really is, as distinguished from that which is only imagined to be, is to be found in its independence of all relation to the experience of a subject. What exists at all, the realist holds, exists equally whether it is experienced or not. Neither the fact of its
- 23. existence nor the kind of existence it possesses depends in any way upon its presence to an experience. Before it was experienced at all it had just the same kind of being that it has now you are experiencing it, and it will still be the same when it has passed out of experience. In a word, the circumstance that a mind—whether yours or mine or God’s is indifferent to the argument—is aware of it as one of the constituents of its experience, makes no difference to the reality of the real thing; experience is what is technically called a relation of one-sided dependence. That there may be experience at all, and that it may have this or that character, there must be real things of determinate character, but that there may be real things, it is not necessary that there should be experience. This is, in brief, the essence of the realist contention, and any philosophy which accepts it as valid is in its spirit a realist philosophy. As to the number and nature of the supposed independent real things, very different views may be held and have been held by different representatives of Realism. Thus some realists have maintained the existence of a single ultimate reality, others of an indefinite plurality of independent “reals.” Parmenides, with his doctrine that the real world is a single uniform unchanging material sphere, is an instance in the ancient, and Mr. Herbert Spencer, with his Unknowable, an instance in the modern world of a realist of the former or “monistic” type. The ancient atomists, and in more recent times Leibnitz with his infinite plurality of independent and disconnected monads, and Herbart with his world of simple “reals,” afford the best known instances of a doctrine of pluralistic Realism. So again, the most diverse theories have been propounded as to the nature of the “reals.” Ancient and modern atomists have thought of them as material, and this is perhaps the form of realistic doctrine which appeals most readily to the ordinary imagination. But though a materialistic metaphysician is necessarily a realist, a realist need not be a materialist. Herbart thought of the independent “reals” as qualitatively simple beings of a nature not capable of further definition, Leibnitz as minds, while Agnostic philosophers of the type of Spencer conceive their ultimate reality as a sort of neutral tertium quid, neither mental nor material. The only point on which all the theories agree is that the reality of that which they recognise as true
- 24. Being consists in its not depending for its existence or its character on relation to an experience. The differences of detail as to the number and nature of independent “reals,” though of great importance for our complete estimate of an individual realist’s philosophical position, do not affect our general verdict on the tenability of the first principle of Realism. The one point of divergence among realists which may be considered as of more than secondary importance for our present purpose, is the difference between what we may call Agnostic and Dogmatic Realism. Agnostic Realism, while asserting the ultimate dependence of our experience upon a reality which exists independently of experience, denies that we can have any knowledge of the nature of this independent reality. The independent reality by which all experience is conditioned is, on this view, an Unknowable or Thing-in-itself,[43] of which we are only logically entitled to say that it certainly is, but that we do not in the least know what it is. The doctrine of Agnostic Realism has probably never been carried out by any thinker with rigid consistency, but it forms a leading feature of the philosophy of Kant as expounded in his First Critique, and through Kant has passed into English thought as the foundation of the systems of Sir William Hamilton and Mr. Herbert Spencer.[44] Dogmatic Realism, of which Leibnitz and, at a later date, Herbart are the most important representatives in modern philosophy, on the contrary, while maintaining that real being is independent of experience, at the same time holds that it is possible to have positive knowledge not only of its existence but of its nature. In principle, both these forms of Realism have been already excluded by the argument of Book I. chap. 2, § 4. The supreme importance of the principle on which the argument rests may perhaps warrant us in once more briefly recurring to it. Our reasoning, it will be remembered, took the form of a challenge. Produce any instance you please, we said to the realist, whom we had not then learned to know by that name, of what you personally regard as reality, and we will undertake to show that it derives its reality for you from the very fact that it is not ultimately separable from the experience of a subject. A thing is real for you, and not merely imaginary, precisely because in some aspect of its
- 25. character it enters into and affects your own experience. Or, what is the same thing in other words, it is real for you because it affects favourably or otherwise some subjective interest of your own. To be sure, the thing as it enters into your experience, as it affects your own subjective interests, is not the thing as it is in its fulness; it only touches your life through some one of its many sides. And this may lead you to argue that the real thing is the unexperienced “condition” of a modification of your experience. But then we had again to ask what you mean by saying that facts which you do not experience are real as “conditions” of what you do experience. And we saw that the only meaning we could attach to the reality of the “condition” was presence to an experience which transcends your own. To this general argument we may add two corollaries or supplementary considerations, which, without introducing anything fresh, may help to make its full force more apparent. (1) The argument, as originally presented, was concerned directly with the that of reality, the mere fact of its existence. But we may also state it, if we please, from the side of the what, the nature possessed by the real. You cannot affirm any doctrine about the real existence of anything without at the same time implying a doctrine about its nature. Even if you say “Reality is unknowable,” you are attributing something beyond mere independence of experience to your reality; you are asserting that what is thus independent possesses the further positive quality of transcending cognition. Now what, in logic, must be your ground for attributing this rather than any other quality to your independent reality? It can only be the fact or supposed fact—which is indeed regularly appealed to by the Agnostic as the foundation of his belief—that our experiences themselves are all found to be self-contradictory. There is no ground for taking the unknowability of Reality to be true unless you mean by it a character which belongs not to something which stands outside all experience, but to experience itself. The same contention applies to any other predicate which the realist affirms as true of his ultimate reality. (2) Again, we may with effect present our argument in a negative form. Try, we may say, to think of the utterly unreal, and see how you will have to conceive it. Can you think of sheer unreality otherwise
- 26. than as that of which no mind is ever aware, of which no purpose has ever to take account as a condition of its fulfilment? But to think of it thus is to attribute to it, as its definition, precisely that independence in which the realist finds the mark of ultimate reality. And if “independence” constitutes unreality, presence to and union with experience must be what constitutes reality. Yet, however fatal this line of argument may be to the principle of the realistic contention, we ought not to be satisfied with such a mere general refutation. We must try to see what is the element of truth in the realistic views to which they owe the plausibility they have always possessed for minds of a certain type. In Philosophy we are never really rid of an error until we have learned how it arises and what modicum of truth it contains. (1) Agnostic Realism. We may begin with Agnosticism, with which we ought now to have no serious difficulty. Agnostic Realism, as we have seen, is in principle a doubly self-contradictory theory. For it combines in one breath the irreconcilable declarations that the reality of things is unknowable and that it knows it to be so.[45] Further, as we have just said, it makes alleged contradictions which only exist in and for experience, its sole ground for affirming that something, of which we can only specify that it is outside all experience, transcends cognition. To have grasped these two points is to have disposed of Agnosticism as a metaphysical theory. Yet with all its defects Agnosticism still enshrines one piece of truth which the metaphysician is peculiarly prone to forget. Of all men the metaphysician, just because his special interest is to know something final and certain about Reality, is the most apt to exaggerate the amount of his certain knowledge. It is well to be reminded that the certainty with which we may say that Reality is experience is compatible with a very imperfect and limited theoretical insight into experience itself. In actual life this is a far from unfamiliar fact; the literature of common sense is full of observations to the effect that we never really know our own hearts, that the most difficult task of the sage is to understand himself, and so forth,— complaints which all turn on the point that even our own limited direct experience of our own meanings and purposes goes far beyond what we can at any moment express in the form of reflective
- 27. knowledge. Yet it is easy, when we come to deal in Metaphysics with the nature of ultimate Reality, to forget this, and to suppose that the certainty with which we can say that the ultimately Real is an experience justifies us in wholesale dogmatising about the special character of that experience. As a protest against such exaggerated estimates of the extent of our theoretical knowledge of the nature of Reality, Agnosticism thus contains a germ of genuine and important truth, and arises from a justifiable reaction against the undue emphasising of the merely intellectual side of our experience, of which we have already seen, and shall hereafter still more fully see, ground to complain as a besetting weakness of the metaphysically minded. (2) Dogmatic Realism, that is, Realism with admittedly knowable independent “reals,” is a much more workable doctrine, and in one of its forms, that of the so-called “naïve realism” which supposes the world of experienced things with all its perceived qualities to exist independently of any relation to an experiencing subject in precisely the same form in which we experience it, fairly represents the ordinary views of unphilosophical “common-sense” men. Nothing seems more obvious to “common sense” than that my perception of a thing does not bring it out of nothing into existence, and again does not create for it new qualities which it had not before. It is because the thing is already there, and has already such and such a nature, says “common sense,” that I perceive it as I do. Therefore the whole world of perceived things must exist independently in the same form in which they are perceived, as a condition of my perception of them. When this view comes to be worked out as a philosophical theory, it usually undergoes some transformation. The fact of illusion, and the experimentally ascertained subjective differences between individual percipients,[46] or between different states of the same percipient, make it hard for the realist who wishes to be scientific to maintain that all the perceived qualities of experienced things are equally independent of the experiencing subject. Reflection usually substitutes for the “naïve” realism of everyday life, a theory of “scientific” realism according to which the existence and some of the known properties of the experienced world are independent of the experiencing subject, while others are regarded as mere secondary
- 28. effects arising from the action of an independent reality on the subject’s consciousness. With the further differences between the various types of scientific realism, according to the special properties which are held to belong to things independently of the percipient subject, we are not at present concerned.[47] It is, of course, clear that our general argument against the existence of any reality except as in an experience tells just as much against “naïve” realism and its more reflective outgrowth “scientific” realism as against Agnosticism. But the very plausibility and wide diffusion of realistic views of this type make it all the more necessary to reinforce our contention by showing what the truth Realism contains is, and just where it diverges from truth into fallacy. Nor is it specially difficult to do this. The important elements of truth contained in Realism seem to be in the main two. (i) It is certain that a thing may be real without being consciously present as a distinguishable aspect in my experience. Things do not begin to exist when I begin to be aware of them, or cease to exist when I cease to be aware of them. And again, the fact that I make mistakes and am subject to illusion shows that the qualities of things are not necessarily in reality what I take them to be. (2) Further, as is shown by the fact of my imperfect understanding of my own feelings and purposes, something may actually be an integral part of my own life as an experiencing subject without my clearly and consciously recognising it as such when I reflect on the contents of my experience. But precisely how much do these two considerations prove? All that is established by the first is the point on which we have already insisted, that it is not my experience which constitutes Reality; and all that is established by the second, that experience, as we have already repeatedly seen, is not merely cognitive. But the admission of both these positions brings us not one step nearer the conclusion which the realist draws from them, that real existence is independent of all experience. Because it is easy to show that the reality of a thing does not depend on its being explicitly recognised by any one finite percipient or any aggregate of finite percipients, and again, that there is more in any experience of finite percipients than those percipients know, the realist thinks he may infer that there are
- 29. realities which would still be real though they entered into no experience at all. But there is really no logical connection whatever between the premisses of this inference and the conclusion which is drawn from them. This may be made clearer by a couple of examples. Take, to begin with, the case of the mental life of my fellow human beings. And, to state the case in the form in which it appears most favourable to the realist conclusion, let us imagine an Alexander Selkirk stranded on a barren rock in the midst of the ocean. The hopes and fears of our Selkirk are independent of my knowledge of them just as completely and in just the same sense in which the existence and conformation of the rock on which he is stranded are so. I and all other inhabitants of the earth may be just as ignorant of Selkirk’s existence and of what is passing in his mind as we are of the existence and geological structure of his rock. And again, what Selkirk explicitly cognises of his own inner life may bear as small a proportion to the whole as what he explicitly cognises of the properties of his rock to the whole nature of the rock. Yet all this in no wise shows that Selkirk’s hopes and fears and the rest of his mental life are not experience or have a reality “independent of experience.” Hopes and fears which are not experience, not psychical matter of fact, would indeed be a contradiction in set terms. And what the argument fails to prove of Selkirk’s mental life, it fails, for the same reason, to prove of Selkirk’s rock. We may pass from the case of the mental life of a fellow-man to the case of unperceived physical reality. A recent realist philosopher, Mr. L. T. Hobhouse, has brought forward as a clear instance of an independent physical reality, the case of a railway train just emerging from a tunnel. I do not perceive the train, he says, until it issues from the tunnel, but it was just as real while it was running through the tunnel. Its reality is therefore independent of the question whether it is perceived or not. But, in the first place, the argument requires that the train shall be empty; it must be a runaway train without driver, guard, or passengers, if the conditions presumed in the premisses are to be fulfilled. And, in the second place, we may retort that even an empty runaway train must have been despatched from somewhere by somebody. It must stand in some relation to the
- 30. general scheme of purposes and interests expressed in our system of railway traffic, and it is precisely this connection, with a scheme of purposes and interests, which makes the runaway train a reality and not a mere fiction of an ingenious philosopher’s imagination. If Mr. Hobhouse’s argument proves the independent reality of the train in the tunnel, it ought equally to prove, and does equally prove, the independent existence of Selkirk’s fluctuations from hope to despair and back again on his isolated rock. And precisely because it proves both conclusions equally, the sort of independence it establishes cannot be independence of experience. Like all realist arguments, it turns on the identification of experience with the cognitive aspect of experience, an identification too often suggested by the language of the “idealists” themselves.[48] § 8. The persistent vitality of Realism is due to its protest against the fallacies of an opposing theory which has of late especially found favour with some distinguished students of natural science, and which we may conveniently call Subjectivism.[49] Realism, as we saw, started from the true premisses, that there are real facts of which my experience does not make me explicitly aware, and that my cognition even of my own experience is incomplete, and argued to the false conclusion that there are therefore realities independent of any experience. Subjectivism reasons in the opposite way. It asserts truly that there is no reality outside experience, and then falsely concludes that I can know of no reality except my own cognitive states. Its favourite formula are expressions such as, “We know only the modifications of our own consciousness,” “All we know is our own perceptions,” “Nothing exists but states of consciousness.” These formulæ are not all obviously identical in meaning, but the exponents of Subjectivism seem to use them without any conscious distinction, and we shall probably do the theory no injustice if we criticise it on the assumption that the expressions are meant to be of identical signification. Now it is clear that the logical consequences of the subjectivist doctrine are so subversive of all the practical assumptions upon which daily life is based, that they should require the most stringent proof before we give our assent to them. If Subjectivism is true, it follows immediately that not merely the “whole choir of heaven and
- 31. furniture of earth,” but the whole of humanity, so far as I have any knowledge of its existence, is a mere subjective affection of my own “consciousness,” or, as the scientific subjectivist usually, for some not very obvious reason, prefers to say, of my own brain. Every argument which the subjectivist can produce to show that “things” are, for my knowledge at any rate, “modifications of my own consciousness,” applies to the case of my fellow-men with as much force as to the case of the inorganic world. The logical inference from the subjectivist’s premisses, an inference which he is rarely or never willing to draw, would be that he is himself the sole real being in a world of phantoms, not one of which can with any certainty be said to correspond to a real object. And conversely, any valid ground for recognising the existence of my fellow-men as more than “states of my own consciousness,” must equally afford ground for admitting the reality, in the same general sense, of the rest of the world of things familiar to us from the experiences of everyday life.[50] For if any one of the things composing the world of practical life has a reality which is not dependent upon its presence to my particular experience, then there is the same reason for believing that every other such thing has a like reality, unless there happen to be special grounds for regarding the perception to which it is present as an hallucination. We must not, however, simply dismiss the subjectivist theory in this summary way. We must examine the doctrine in detail sufficiently to discover where the fallacy comes in, how it arises, and what modicum of sound philosophic insight it may possibly contain. To take these three points in logical order— (a) The current arguments for Subjectivism are often so stated as to confuse together two quite distinct positions. When it is said that what we perceive is “our own subjective states,” the meaning intended may be either that there is, at least so far as I am able to know, no real existence in the universe except that of my “states of consciousness”; or again, that there are such realities, but that the properties which I perceive do not belong to them in their own nature but are only subjective effects of their action upon my “consciousness,” or, if you prefer to speak in physiological language upon my nervous system. Now, many of the arguments commonly
- 32. urged by the subjectivist would at most only prove the second conclusion, in which the subjectivist agrees to a large extent with the scientific realist. Thus it is an ignoratio elenchi to reason as if the facts of hallucination, illusion, and discrepancy between the reports of different percipients or different sense-organs of the same percipient gave any support to the special doctrine of Subjectivism. These facts, which, as we have seen, are equally appealed to by scientific realists, prove no more than that we do not always perceive the world of things as it is, and as it must be thought of if we would think truly,—in other words, that there is such a thing as error. Now the problem “How is it possible for us to think or perceive falsely?” is, as the student of Greek philosophy knows, both difficult and important. But the existence of error in no way shows that the things which I perceive are “states of my own consciousness”; on the contrary, error is harder to explain on the subjectivist theory than on any other. For if what I perceive has some kind of existence distinct from the mere fact of my perceiving it, there is at least a possibility of understanding how the reality and my perception of it may be discrepant; but if the existence of a thing is only another name for the fact that I perceive it, it seems impossible that I should perceive anything except as it is. On the subjectivist theory, as Plato showed in the Theaetetus, every percipient being ought, at every moment of his existence, to be infallible. We may confine our attention, then, to the grounds which the subjectivist alleges for the former conclusion, that nothing can be known to exist except my own “states of consciousness,” and may dismiss the whole problem of erroneous perception as irrelevant to the question. Now the general argument for Subjectivism, however differently it may be stated by different writers, consists, in principle, of a single allegation. It is alleged as a fact in the Psychology of cognition, that things are immediately perceived by us as modifications of our own sensibility, or “states of our own consciousness,” and that it is therefore impossible to get behind this ultimate condition of all perception. Against this psychological doctrine we have to urge (1) that it is in flagrant contradiction with the certain facts of actual life; and (2) that, as a doctrine in Psychology, it is demonstrably false.
- 33. (1) There are certain realities, admitted by the subjectivist himself, which are manifestly not “states of my consciousness,” and of which I yet, as the subjectivist himself admits, have a genuine though imperfect knowledge; such realities are, e.g., the ends and purposes of my fellow-men, and again many of my own ends and purposes. It is allowed on all hands that I can know not only the fact of the existence of other men, but also, to some extent at least, the character of their various purposes and interests. This is involved, for instance, in the simple fact that when I read a letter it is normally possible for me to understand the writer’s meaning. It is equally involved in the fact that I can know the truth of any ordinary historical matter of fact, e.g., the date of the great fire of London. Neither the date of the fire of London nor the meaning of my correspondent’s sentences is a “state of my consciousness” in any intelligible sense of the words, yet both are typical instances of the kind of facts of which our ordinary knowledge of the world of everyday life and practice wholly consists. And what is true of facts relating to the deeds and purposes of others is equally true of my own deeds and purposes. The facts which make up my own life cannot, without violence to language, be reduced to “states of my consciousness.” For instance, I may know that I have a certain temperament or disposition, e.g., that I am irascible by temperament or of a sentimental disposition; but though my knowing these truths about myself may in a sense be called a state of my consciousness, the truths themselves cannot be called “states of my consciousness” without a serious logical fallacy of equivocal middle term. (2) This will be made clearer by a consideration of the psychological principle invoked by the subjectivist. What the subjectivist means when he says that in perception I am aware only of the states, or subjective modifications, of my own consciousness, is that the object of which each perceptive state is aware is simply itself as a perceptive state; the perception perceives itself and nothing else. E.g., when I say I see red, what I am really aware of is that I am in a state of perceiving red; when I say I hear a noise, what I am aware of is that I am in a state of hearing a noise, and so universally. Now this is so far from being a truth, that it is absolutely and demonstrably false. We may, in fact, definitely lay it down that
- 34. the one thing of which no one, except the introspective psychologist, is ever aware is his own perceptive state in the act of perceiving, and that, even in the case of the psychologist who sets himself purposely to study his own states, no perceptive state ever perceives itself. What I am aware of when I look at a red surface is not “myself-as- perceiving-red,” but the splash of red colour itself. When I see a man, I do not perceive “myself-as-seeing-a-man,” but I perceive the other man. So when I take a resolution to act in a certain way or realise that I am in a certain mood, what I am directly aware of is not “myself-as-forming-the-resolution” or “myself-as-in-the-mood,” but the resolution or the mood. Even when, as an introspective psychologist, I sit down to study the formation of resolutions or the peculiarities of emotional moods by reflection on my own experience, the state in which I study the formation of a resolution or the nature of a mood is not itself the state of resolving or of experiencing the mood in question. We cannot too strongly insist that, if by “self- consciousness” is meant a cognitive state which is its own object, there is no such thing, and it is a psychological impossibility that there should be any such thing, as self-consciousness. No cognitive state ever has itself for its own object. Every cognitive state has for its object something other than itself.[51] Even where I make an assertion about my subjective condition, as when I say “I know I am very angry,” the state of knowing about my feeling is as distinct from the feeling itself as the state of knowing that I see red is from the red colour that I see. What the subjectivist does is to confuse the two. Because the act of knowing is itself a state of the knowing subject, and because in some cases the knowledge may again have reference to some other state of the same subject, he infers that what I know at any moment is my own subjective condition in the act of knowing. In other and more technical words, he confuses the cognitive act or state with its own object. To what absurd results this confusion would lead him, if he were logical in the inferences he makes from it, we have already seen. We can now see that psychologically the confusion is a double one. (1) The subjectivist confuses experience with mere awareness of a presented content. He ignores the presence of the true “subjective” factor of selective attention throughout experience, and
- 35. is thus led to forget that all experiences imply an element which is in the experiencing mind but not presented to it. (2) And in confining his attention to the presentational aspect of experience, he goes on to confound the presented content with the fact of its presentation. As against this second confusion it is essential to a true theory of knowledge to emphasise three points of distinction between the presented content or object of a cognitive state and the state itself, considered as a process in the history of an experiencing subject. (1) The cognitive state is never its own object, it refers to or cognises an object distinct from its own existence as a psychical occurrence. This is the truth which Realism distorts into the doctrine that the object of knowledge must have a reality of “independent of” experience. (2) The object of knowledge is never created by the occurrence of the psychical state in which a particular percipient becomes aware of its existence. This is just as true of so-called “merely ideal” objects as of physical things. The properties of the natural logarithms or of the circular functions in trigonometry are just as independent of my knowledge of them as the qualities of the trees and animals I should see if I turned from my writing desk and looked out at the window. (3) The object of knowledge has always a character of which only a fragment is ever presented to my perception or reflection in any cognitive state. Every cognitive state refers to or stands for a great deal more than it directly means to me. (3) The origin of the subjectivist fallacy, as has been brilliantly shown by Avenarius,[52] is to be found in the “intrasubjective intercourse” of a plurality of percipients capable of communicating their experience to each other. So long as I am dealing solely with myself as an experiencing being and my relation to my own environment, there is no possibility of a subjectivist interpretation. In my own direct experience I have to do neither with “mental states” nor with mere “objects of cognition,” but with things which in various ways by their interference assist or hinder the accomplishment of my various purposes, and of which I have therefore to take note, so as to adapt my ways of reaching my ends to their ways of behaviour. Hence the “natural” view of the world, for a single experiencing being, would be that of “naïve realism,” to which the things forming my environment are real in precisely the same sense in which I am
- 36. real myself. But as soon as I have to take account of the experiences of other percipients, there arises an inevitable fallacy which leads to philosophical consequences of the gravest kind. Starting with the assumption that the things I perceive are the real things, I feel a difficulty as to how the same things can be perceived by the other percipients around me. E.g., if the sun I see is the real sun, what about the sun seen by some one else? Instead of finding the true explanation, that all the percipients are in relation to a common environment which is independent of its presence to any one percipient’s experience, I very naturally fall into the mistake of thinking the things perceived by other men to be “ideas” or “percepts” of the real things perceived by me. These perceptual copies of the real things I, for obvious reasons, locate somewhere “in” the organisms of my fellow-percipients. Then I go on to interpret my own experience in terms of the theory I originally devised to meet the case of my fellow-men, and infer that what I myself perceive is a set of “percepts” or “ideas” produced “in” my organism by a reality “outside” all experience. And it is then an easy step to the final conclusion that, inasmuch as all known and knowable things are mere “ideas in some one’s head,” nothing else exists. Subjectivism is thus the last step in the development of the fallacy which begins with what Avenarius calls “introjection.” Just as we learned that the existence of our fellow-men is the cardinal fact of experience which affords the most immediate refutation of the subjectivist theory, so the original source of the subjectivist fallacy is failure to recognise their experience as being on the same level of reality as our own. (4) We need not say much on the element of truth which Subjectivism preserves in a distorted form. We have seen that, as against Realism, Subjectivism is right in maintaining the indissoluble unity of real being with experience, though it twists this truth into an absurdity by first identifying experience with my own limited and imperfect experience and then giving a false psychological interpretation of the nature of that experience itself. How a reality can be independent of presentation in my experience and yet be in its very nature dependent upon experience for its existence and character, has already been sufficiently illustrated. But we may perhaps say that even in the identification of experience with my own
- 37. experience there is an underlying substratum of genuine philosophic truth. For, as we have more than once insisted, there is manifestly a great deal more in my own experience than what is at any time present as the object of conscious cognition. Or, as Mr. Bradley is fond of putting it, there is always more in my mind than before it. I am never fully aware at any moment even of the full nature of my own purposes and feelings. This is why the deceitfulness of my own heart has become a common-place of religious self-examination as well as of worldly wisdom. Again, every increase of insight into our own real feelings and purposes involves increased insight into the feelings and purposes of the other feeling beings with whom we stand in the various relations of social intercourse.[53] Hence it might fairly be contended that fully to know your own meaning, fully to understand what you want, would imply complete insight into the structure of the whole world of reality, —in fact, that self-knowledge and knowledge of the universe must ultimately be the same thing. The systematic unity of the whole world of experience may be so complete that there is nothing in it anywhere which does not correspond to some element in the experience of every one of its members. Each member may, like the monads of Leibnitz, represent the whole system though at very different levels of coherency and from very different points of view. But such a conception, though it would concede to Subjectivism that whatever forms a part of the system of real being somehow falls within my individual experience, would take as the foundation of its assertion that very distinction between what is implicitly present in my experience and what is explicitly before it which Subjectivism consistently ignores. Whether the doctrine as thus re-stated can be affirmed as more than a fascinating possibility, we shall be better able to judge when we have discussed in our next chapter the systematic unity of Reality. Consult further:—F. H. Bradley, Appearance and Reality, chaps. 13, 14; T. Case, Physical Realism, pt. 1; L. T. Hobhouse, The Theory of Knowledge, pt. 3, chap. 3, The Conception of External Reality; H. Lotze, Metaphysic, bk. i. chap. 7 (pp. 207-231 of vol. i. in Eng. trans.); J. S. Mackenzie, Outlines of Metaphysics, bk. i. chap. 3,
- 38. Theories of Metaphysics; J. Royce, The World and the Individual, First Series (Lecture on the First Conception of Being). 31. See, in particular, Royce, The World and the Individual, Second Series, Lecture 1, for a telling elaboration of this thought. I should note that I do not myself use the term “existence,” as is sometimes done, with special restriction to the sense of presence as a sensible event at a particular point of space and time. When so used, it is, of course, much narrower in scope than the term “Being.” 32. Compare the brilliant but not altogether convincing argument of Professor James, in The Will to Believe. 33. See the whole treatment of question of feeling in Dr. Stout’s Manual of Psychology. I do not, of course, mean that “consciousness of activity” successful or thwarted as a fact precedes and conditions pleasure-pain. On the contrary, it is a familiar fact of experience that we often learn what our purposes are for the first time by the pain which attends their defeat. E.g., a man may first realise that he is, and has been, in love by his pain at his mistress’s preference of a rival suitor. And nothing seems more certain than that many pleasures are quite independent of “actual conation,” as Plato long ago recognised. I must take this opportunity to guard once for all against some plausible misconceptions. (a) When I speak of feeling as “purposive” or “teleological,” I do not mean to make what, to my own mind, would be the monstrous assumption, that it necessarily presupposes conscious anticipation of its guiding end or purpose. All that I mean is that the processes of conscious life are as a matter of fact only intelligible with reference to the results in which they culminate and which they serve to maintain; or again, that they all involve the kind of continuity of interest which belong to attention. (b) If attentive interest is not necessarily actual conation, actual conscious effort, still less is it necessarily actual will. For me, as for Mr. Bradley (see his article in Mind for October 1902), where there is no ideal anticipation of the result of a process there is neither actual desire nor actual will. And since I cannot see that all attention implies ideal anticpation, I certainly could not agree with Prof. Royce that ultimate Reality is simply the “internal meaning of an idea.”
- 39. My own meaning will be made clearer by reference to the illustration given at the beginning of this note. A man first realises that he has been in love because he feels pained at a rival’s success. So far as this is so, I should say, there has been no actual conation, and a fortiori, no actual will or desire. But—and this is my point—he would not feel the pain unless the success of the rival thwarted the successful issue of a specific psychophysical tendency of an essentially forward-reaching or teleological kind. The failure may for the first time make him aware of the presence of the tendency, but it must previously have been there as a condition of its own failure. 34. This qualification has to be added to avoid prejudging the very difficult question whether “position” itself is “relative” or “absolute.” Fortunately our argument is independent of the determination of the problem. Even if there should be differences between points as “absolute” as the difference between red and blue, our contention would retain its force. 35. For otherwise the facts which lay outside the purposes or interests of the Absolute would be “foreign” facts “given” from without and not in systematic harmony with its experience as a whole. The complete systematic unity of all facts would thus fall outside what was to be, ex hypothesi, an all-containing experience. Q.E.A. 36. For further reflections upon the unsatisfactoriness of such a conception of the Absolute as the “union of Thought and Will,” see Bk. IV. chap. 6, § 1, where it is shown that knowledge and will alike, as actual knowledge and actual will, belong only to finite beings. 37. I.e. if will be taken strictly to mean an actual volition, love and a “will to love” cannot co-exist; if we take will improperly to mean a “standing” interest of purpose, the case is different. 38. The student of the history of Philosophy will be reminded of the grounds on which Spinoza objects to ascribe “intellect” and “will” in the proper sense of the terms to his God, as well as of the “knowledge of the third or intuitive kind” and the “infinite intellectual love” of God for Himself which are so prominent in the fifth part of the Ethics. Similar considerations have sometimes led to a preference for the term “organic” rather than “purposive” or “teleological,” as expressive of the ultimate unity of experience. The word “organic,”
- 40. however, might suggest biological conceptions of growth, dependence on an external environment, etc., which would be out of place. But the student may compare with what has been said of the “purposive” character of individuality Spinoza’s conception of the being of a thing as a conatus in suo esse perseverandi. 39. For a full examination of the relation between reality and scientific symbolism, consult Ward, Naturalism and Agnosticism, part 1. The more clearly it is realised that scientific hypotheses are essentially a system of mathematical symbolism, the more impossible it becomes to suppose that they deal directly with the concrete nature of things. 40. In Principles of Human Knowledge, §§ 70-75, Berkeley indeed seems on the very verge of denying that God Himself “perceives” the “ideas” which by His action He excites in us. But at § 139 we find that a “spirit” means “that which perceives ideas, and wills and reasons about them,” and in the third Dialogue it is expressly stated that sensible things are “perceived by God” [Works, Edit. in Bohn’s Libraries, vol. i. p. 368]. In fact, from the psychological standpoint of Berkeleian sensationalism, to deny God’s possession of “ideas” (i.e. sense-contents) would have been tantamount to denying His spirituality. 41. Unfortunately Berkeley, like so many philosophers, thought of “activity” as primarily an external relation between a “cause” and the material on which it “works.” This is probably why he failed to realise the “active” character of the perceptual process. 42. The reader will do well to compare with the whole of the foregoing section the treatment of perception as essentially teleological in Dr. Stout’s Manual of Psychology,3 bk. iii. pt. 1, chap. 2. I need hardly observe that recognition of the fundamental significance of purpose and selection for mental life does not of itself entail the adoption of “voluntarist” views in Psychology. What is fundamental for real mental life may perfectly well admit of analysis into hypothetical simpler elements for the purpose of the psychologist. Thus the admission that all mental life is teleological and selective need not involve the adoption of such metaphysical theories of activity as are adversely criticised by Mr. Bradley in his