Week 2-4 Logic.pdf Introduction to Western Philosophy

INTRODUCTION TO
WESTERN PHYLOSOPHY
TRAN THANH TAM (LL.M, PhD Candidate)
(WEEK 2)

WHY STUDY LOGIC?
(AS A BUSINESS STUDENT)

WHY STUDY LOGIC?
• Doing logic is, in many ways, like ‘going to the gym for your
brain’.
• Distinguish good reasoning from bad reasoning (fallacies).
• Studying logic will just make explicit the rules of inference
(reasoning) that are already a part of your everyday life.
• Whatever your college major or career plans, a strong
foundation in making good inferences (doing logic) will
improve your performance.
• Logic can also be fun!

GROUP PRESENTATION
FALLACIES IN WESTERN PHILOSOPHY
Main topics:
• Fallacies of Relevance (43 forms) (e.g, Ed Hominem, Appeal to
Emotion, Appeal to the people, Straw man, Genetic Fallacy …)
• Fallacies of Ambiguity (16 forms) (e.g, Equivocation, Division,
Composition, Legalistic mistake, oversimplification, …)
• Fallacies of Presumption (34 forms) (e.g, Begging the question,
False Dilemma, Slippery Slope
You should be able to:
• 1- Identify these fallacies in real life
• 2- How to avoid these fallacies
Presentation length: 20mins max, plus 10-min Q &A
Team member: Max 5 ppl each team.

1. BASIC CONCEPTS
• A Claim is a statement, proposition, or declarative
sentence (or parts of declarative sentences)
composed of at least one subject noun phrase and
a finite verb.
• A claim is a sentence that is either true or false—in
other words, typically a declarative sentence or a
sentence component that could stand as a
declarative sentence.
• Questions, proposals, suggestions, commands, and
exclamations usually are not usually classified as
statements.

DISCUSSION
Decide if the following are statements. Answer True or False if possible.
1. Let’s go to a movie tonight.
2. Turn off the TV right now.
3. Chocolate truffles are loaded with calories.
4. Fantastic!
5. Melatonin helps relieve jet lag.
6. Where is Khartoum?
7. Political candidates always tell the complete truth.
8. No wives ever cheat on their husbands.
9. I suggest you get contact lenses.
10. The sun is a cube‐shaped star.
11. Bill Gates wrote War and Peace.
12. A person can stand and sit at the same time, in the same respect.
13. Most children are born with two hands.
14. Margaret Thatcher was the first female Prime Minister of the United
Kingdom.

1. BASIC CONCEPTS
• An argument is made up of at least two claims,
one of which plays the role of the conclusion,
while the other plays the role of a premise.
• A premise is the claim that is supposed to
support, back up, justify, or give a reason for
accepting the conclusion.
• A conclusion is the claim that is supported by,
backed up by, justified by, or shown to be what
follows from the premise.

1. BASIC CONCEPTS
• Example 1:
Premise: Given that Frank is a bachelor.
Conclusion: This shows us that Frank is an
unmarried male.
• Example 2:
Premise: Jane has two apples and two oranges in
her shopping cart.
Conclusion: Thus, Jane has four fruits in her
shopping cart.

Week 2-4 Logic.pdf Introduction to Western Philosophy

PREMISE & CONCLUSION INDICATORS
Premise Indicators:
As, since, for, because, given that, for the reason
that, inasmuch as, in view of the fact assuming
that, due to the fact that, seeing that,…
Conclusion Indicators:
Therefore, hence, thus, so, we may infer, it
follows that, consequently, as a result, this
shows us that, for this reason,…

IDENTIFY THE PREMISES AND CONCLUSION OF THE
ARGUMENT
We must get serious about modernizing our nation’s crumbling infrastructure. Many
of our bridges are practically falling down, and our transit system is in dire need of
repair. Furthermore, making these improvements would create jobs for millions of
workers.
• P1: Many of our bridges are practically falling down.
• P2: Our transit system is in dire need of repair.
• P3: Making these improvements would create jobs for millions of workers.
• C: We must get serious about modernizing our nation’s crumbling infrastructure.

DISCUSSION
Houses in Indonesia sometimes have their electrical outlets in
the middle of the wall rather than at floor level. Why? A
beginning of an explanation is that flooding is a danger in the
Netherlands. Citing this fact does not help much, however,
unless one remembers that Indonesia was formerly a Dutch
colony. We can understand why the Dutch might put their
electrical outlets above floor level in the Netherlands. It is safer
in a country where flooding is a danger. Is flooding, then, a
similar danger in Indonesia? Apparently not; so why did the
Dutch continue this practice in Indonesia? The answer is that
colonial settlers tend to preserve their home customs, practices,
and styles. The Dutch continued to build Dutch-style houses with
the electrical outlets where (for them) they are normally
placed—that is, in the middle of the wall rather than at floor
level.
Restate this explanation in the form of an argument (that is,
specify its premises and conclusion).

CREATE THE FOLLOWING ARGUMENTS
1. An argument having one or more premise indicators and the
conclusion:
“Uniforms should/should not be required in high schools.”
2. An argument having a conclusion indicator and the conclusion:
“The legal drinking age should/should not be lowered to 18.”
3. An argument having no indicator words and the conclusion:
“Renewable forms of energy should/should not be subsidized by
the government.”

CLASSIFICATION OF ARGUMENTS
• Deductive argument: An argument in which the
truth of the premises absolutely guarantees
the truth of the conclusion
• Inductive argument: An argument where the
truth of the premises gives good reason to
believe the conclusion, but does not absolutely
guarantee the truth of the conclusion.

DEDUCTIVE ARGUMENT:
VALID OR INVALID?
• A valid deductive argument is an argument in
which it is impossible for the conclusion to be
false given that the premises are true.
• An invalid deductive argument is a deductive
argument in which it is possible for the
conclusion to be false given that the premises
are true.

DEDUCTIVE ARGUMENT:
VALID OR INVALID?
• When the conclusion does not follow from the
premises, we say that the argument is invalid.
• When we can show that the premises do lead
to the conclusion, we say that the argument is
valid.

VALID OR INVALID?
• Abortion is the destruction of a human fetus and
the destruction of a fetus is the taking of a
human life. So if the taking of a human life is
murder, then so is abortion.
• All spiders have six legs. All six-legged creatures
have wings. Therefore, all spiders have wings.

VALID OR INVALID?
• Argument 1
1. It’s wrong to take the life of an innocent person.
2. Abortion takes the life of an innocent person.
3. Therefore, abortion is wrong.
• Argument 2
1. All dogs are mammals.
2. Rex is a dog.
3. Therefore, Rex is a mammal.

VALID OR INVALID?
• Argument 3
1. All automakers are computer manufacturers.
2. Vietnam Airlines is an automaker.
3. Therefore, Vietnam Airlines is a computer
manufacturer.
• Argument 4
1. All banks are financial institutions.
2. Prudential is a financial institution.
3. Therefore, Prudential is a bank.

VALID OR INVALID?
• Argument 5
1. Computers can calculate things.
2. The mind can calculate things, too.
3. Therefore, the mind is a computer.

DEDUCTIVE ARGUMENT:
SOUND AND UNSOUND
• A sound argument is a deductive argument that
is valid and has all true premises.
• An unsound argument is a deductive argument
that is invalid, has one or more false premises,
or both.

INDUCTIVE ARGUMENT:
STRONG OR WEAK?
• a strong inductive argument is an inductive
argument in which it is improbable that the
conclusion be false given that the premises are
true. In such arguments, the conclusion does in
fact follow probably from the premises.
• a weak inductive argument is an argument in
which the conclusion does not follow probably
from the premises, even though it is claimed to.

STRONG OR WEAK
Argument 1:
• This barrel contains 100 apples.
• Three apples selected at random were found to be
ripe.
• Therefore, probably all 100 apples are ripe.
Argument 2:
• This barrel contains 100 apples.
• Eighty apples selected at random were found to be
ripe.
• Therefore, probably all 100 apples are ripe.

INDUCTIVE ARGUMENT:
COGENT OR UNCOGENT?
• A cogent argument is an inductive argument
that is strong and has all true premises.
• An uncogent argument is an inductive argument
that is weak, has one or more false premises,
fails to meet the total evidence requirement, or
any combination of these.

DEDUCTIVE VS INDUCTIVE
1. No e-mail messages are eloquent creations. Some love letters are eloquent creations. Therefore,
some love letters are not e-mail messages.
2. Paying off terrorists in exchange for hostages is not a wise policy, since such action will only lead
them to take more hostages in the future.
3. The Wall Street Journal has an article on the new banking regulations. The Financial Times, like the
Wall Street Journal, is a highly respected business publication. Therefore, the Financial Times
probably also has an article on the new banking regulations.
4. World-renowned physicist Stephen Hawking says that the condition of the universe at the instant of
the big bang was more highly ordered than it is today. In view of Hawking’s stature in the scientific
community, we should conclude that this description of the universe is correct.
5. When the Romans occupied England, coal was burned. Since coal produces quite a bit of soot and
sulfur dioxide, there must have been days almost 2,000 years ago when the air in the larger towns
was badly polluted.
6. The Simpson incident had shown me that a dog was kept in the stables, and yet, though someone
had been in and had fetched out a horse, he had not barked enough to arouse the two lads in the
loft. Obviously the midnight visitor was someone whom the dog knew well.
7. Animals that live on plant foods must eat large quantities of vegetation, and this consumes much of
their time. Meat eaters, by contrast, have no need to eat so much or so often. Consequently, meat-
eating hominines [early humans] may have had more leisure time available to explore and
manipulate their environment; like lions and leopards, they would have time to spend lying around
and playing.

FOUR VALID ARGUMENT FORMS
MODUS PONENS
MODUS TOLLENS
HYPOTHETICAL SYLLOGISM
DISJUNCTIVE SYLLOGISM

MODUS PONENS (MP)
• MP could be described as affirming the antecedent
(in P → Q, P is the antecedent, Q the consequent)

MODUS PONENS (MP)
• Argument 1:
Whenever the leading business indicators show a decline
for two successive months, we are in a recession. Since
they have declined during the past two months, we can
conclude that we are now in a recession.
• Argument 2:
If twelve million children die yearly from starvation, then
something is wrong with food distribution.
Twelve million children die yearly from starvation.
Therefore, something is wrong with food distribution.

MODUS TOLLENS (MT)
• MP could be described as denying the consequent

MODUS TOLLENS (MT)
• Argument 1:
If it rains, then the streets get wet.
The streets didn’t get wet.
Therefore, it hasn’t rained.
• Argument 2:
If Japan cares about endangered species, then it has
stopped killing whales.
Japan has not stopped killing whales.
Therefore, Japan does not care about endangered
species

HYPOTHETICAL SYLLOGISM (HS)
• A syllogism is a deductive argument with two premises and a
conclusion
• Hypothetical syllogism consists of two premises and one
conclusion, all of which are hypothetical (conditional)
statements

HYPOTHETICAL SYLLOGISM (HS)
• Argument 1: If I get an A on the midterm, I will ace the
course. Furthermore, if I ace the course, I will graduate
with a 4.0 grade point average. So, it seems that if I get
an A on the midterm, I will graduate with a 4.0.
• Argument 2: If world population continues to grow,
then cities will become hopelessly overcrowded. If
cities become hopelessly overcrowded, then pollution
will become intolerable. Therefore, if world population
continues to grow, then pollution will become
intolerable.

DISJUNCTIVE SYLLOGISM (DS)
The argument form involves the use of statements involving an
either/or choice, symbolized by v as in P v Q, which means
“either P or Q, or both.

DISJUNCTIVE SYLLOGISM (DS)
• Argument 1: Either Macbeth or his wife is
mad. Since Lady Macbeth obviously is not
mad, Macbeth must be mad.
• Argument 2: Either Harvard or Princeton is in
New Jersey. Harvard is not in New Jersey.
Therefore, Princeton is in New Jersey.

AFFIRMING THE CONSEQUENT (AC)
• Argument 1:
If it rains, then the streets get wet.
The streets didn’t get wet.
Therefore, it hasn’t rained.
Argument 2:
If Napoleon was killed in a plane crash, then
Napoleon is dead.
Napoleon is dead.
Therefore, Napoleon was killed in a plane crash.

DENYING THE ANTECEDENT
(DA)
• Argument 1:
If this is a psychology textbook, it will be used in
college classrooms.
This is not a psychology textbook.
So, it won’t be used in college classrooms.
Argument 2:
If Napoleon was killed in a plane crash, then
Napoleon is dead.
Napoleon was not killed in a plane crash.
Therefore, Napoleon is not dead.

DISCUSSION
Create the following arguments:
1. A modus ponens about social media
2. A modus tollens relating to sports
3. A disjunctive syllogism concerning political parties
4. A hypothetical syllogism dealing with the Middle East
5. An affirming the consequent relating to North Korea
6. A denying the antecedent about privacy rights

DISCUSSION
1. A Boeing 757 crashed into the Pentagon on 9/11 only if two giant engines were found
outside the building. It is not the case that two giant engines were found outside the
building. Therefore, a Boeing 757 did not crash into the Pentagon on 9/11.
2. Either the wealthiest people are the happiest, or it is not the case that money can
buy everything. The wealthiest people are not the happiest. Therefore, money cannot
buy everything.
3. Nano-thermite is present in the debris from the World Trade Center. But if that is so,
then the buildings were brought down by controlled demolition. Therefore, the
buildings were brought down by controlled demolition.
4. If Mexico does not get its population growth under control, then its unemployment
problem will never be solved. Mexico’s unemployment problem will never be solved.
Therefore, Mexico will not get its population growth under control.
5. If sea levels rise twenty feet worldwide, then coastal cities from New York to Sydney
will be inundated. If the ice sheets on Antarctica slip into the sea, then sea levels will
rise twenty feet worldwide. Therefore, if the ice sheets on Antarctica slip into the sea,
then coastal cities from New York to Sydney will be inundated.

DISCUSSION
The following selections were taken from letters-to-the-editor newspaper columns. Each
contains one or more arguments, but the exact form of the argument may be hidden or
ambiguous. Use the argument forms presented in this section to structure the selections as
specifically named arguments.
1. There is a simple way to put a big dent in the national human-organ shortage: Allocate
organs first to the people who have agreed to donate their own. Giving organs first to
registered donors would persuade more people to register, and that would make the
allocation system fairer. People who aren’t willing to share the gift of life should go to the end
of the waiting list.
(David J. Undis)
2. Most educators believe math instructors ought to emphasize group problem solving. If
group problem solving is so important (and I think it is), why do we place such emphasis on
individual testing? The national math test is a mistake.
(Frederick C. Thayer)
3. We cannot afford to close the library at Central Juvenile Hall. These young people, in
particular, need to have access to ideas, dreams, and alternative ways of living. It can make
the difference for many students who might become interested in reading for the first time in
their lives while in Juvenile Hall.
(Natalie S. Field)
4. More than a million adult videos are rented each week. Nor, as the propagandists would
have you believe, does viewing such material lead to violent sex crimes. If it did, there would
be over one million such crimes per week.

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