___reason.ppt
- 1. ‘The madman is not the man who has lost his reason. The madman is the man who has lost everything but his reason.’ Thanks to: Richard van de Lagemaat, Cambridge University Press Downloaded on 12th June 2011
- 2. Body in the Park A body is discovered at Jerudong park in the middle of the hot season. It has a fractured skull and many other broken bones, but the cause of death was hypothermia. Can you explain? He was a stowaway hiding in the landing gear of an aircraft. He fell out when the wheels opened for landing at Brunei airport.
- 3. Guilty Sister A woman has incontrovertible proof in court that her husband was murdered by her sister. The judge declares, "This is the strangest case I've ever seen. Though it's a cut-and-dried case, this woman cannot be punished." Why? Her sister is her conjoined twin.
- 4. Deadly Shoes A woman buys a new pair of shoes, goes to work, and dies. She works as an assistant to a knife- thrower at the circus. The shoes have high heels. The knife thrower blindfolds himself and throws as normal, hitting the woman.
- 5. Two men enter a bar. They are served identical drinks. One lives; the other dies. The drinks contain poisoned ice cubes. One mans drinks his drink quickly before the ice melts. Gavin and Pete
- 6. Rationalism Rationalists believe that reason is the most important source of knowledge Because it seems to give us some certainty.
- 7. Don’t scream! You have 45 minutes to write a short essay entitled – “Which of our faculties is more reliable – reason or perception?”. You must give examples and reasons
- 8. Deductive and Inductive reasoning Deductive Reasoning goes from the General to the Particular Inductive Reasoning goes from the Particular to the General
- 9. Deductive vs. Inductive Deduction Induction Definition Reasoning from general to particular Reasoning from particular to general Example All metals expand when heated A is a metal Therefore, A expands when heated Metal A expands when heated Metal B expands when heated Metal C expands when heated Therefore all metals expand when heated Value More certain, but less informative More informative, but less certain
- 11. The curious incident An expensive racehorse has been stolen. I’ve been stolen, that’s why I’ve got such a long face!
- 12. A policeman talks to Sherlock Holmes. The curious incident Does any aspect of the crime strike you as significant Mr Holmes? Yes constable, the curious incident of the dog in the night.
- 13. A policeman talks to Sherlock Holmes. The curious incident The dog did nothing in the night Sir. That is the curious incident!
- 14. Who stole the horse?
- 15. Holme’s reasoning The solution to the crime hinges on the fact that the guard dog did not bark in the night, and from this Holmes deduces that the thief must have been known to the dog. I know him!
- 16. Holmes’ reasoning Holmes’ reasoning can be laid out as follows Guard dogs bark at strangers The guard dog did not bark at the thief Therefore the thief was not a stranger This is an example of gaining knowledge by reasoning. Discuss in your groups the benefits of gaining knowledge by this way.
- 17. Syllogisms Holmes reasoning is an example of a syllogism.
- 18. Syllogisms contain: • Two premises and a conclusion • Three terms, each must occur twice (“Socrates”, “human being”, “mortal”.) • Quantifiers, such as “all”, or “some” or “no” which tell us of the quantity being referred to The Socrates Syllogism • All human beings are mortal • Socrates is a human being • Therefore Socrates is mortal premises conclusion Rationalism A branch of philosophy which takes reason as the most important source of knowledge
- 19. Truth and validity All hippopotamuses eat cockroaches Mr Free is a hippopotamus Therefore Mr Free eats cockroaches Both premises and conclusion are false, but the argument is valid. Imagine that some strange planet exists where the premises are true An argument is valid if the conclusion follows logically from the premises.
- 20. Truth and validity All rats are teachers Mr Free is a rat Therefore Mr Free is a teacher = The premises are both false (although the conclusion is true!) but the argument is still valid.
- 21. Deductive reasoning and truth • Just because an argument is valid (Some IB staff are from Scotland All Scots love eating Haggis Therefore some IB staff love eating Haggis) • Does not mean that the conclusion is true.
- 22. Deductive reasoning and truth For an argument to be true you must be able to answer “yes” to the following questions: • Are the premises true? • Is the argument valid?
- 23. Messi • Messi is a man • All men are mortal • Therefore Messi is mortal The conclusion is only true if the premises are true.
- 24. Make up your own VALID syllogisms to illustrate each of the following; 2 true premises and a true conclusion 1 true premise, 1 false premise and a true conclusion 1 true premise, 1 false premise and a false conclusion 2 false premises and a true conclusion 2 false premises and a false conclusion
- 25. Belief Bias? • Democrats are in favour of free speech • Dictators are not democrats • Therefore dictators are opposed to free speech
- 26. Deciding whether a syllogism is valid Trying to decide if a syllogism is valid is not easy. Venn diagrams can help (at last a good use for Venn diagrams!)
- 27. • Some IB staff are from Scotland • All Scots love eating Haggis • Therefore some IB Staff love eating Haggis Is this a valid argument? Mmmm … Hagis! Deciding whether a syllogism is valid Typical IB staff from Jerudong International School
- 28. Using Venn diagrams • Some IB staff are from Scotland IB Staff Scots IB Staff who are Scottish
- 29. • All Scots like eating Haggis IB Staff Scots Like eating Haggis Using Venn diagrams
- 30. • Therefore some IB staff like eating haggis IB Staff Scots Like eating Haggis Using Venn diagrams
- 31. Another example • All As are Bs • All Bs are Cs • Therefore all Cs are As
- 32. Another example • All As are Bs A B
- 33. Another example • All Bs are Cs A B C
- 34. Another example • Therefore all Cs are As A B C These Cs are not As The syllogism is not valid
- 35. Another example! • All As are Bs • Some As are Cs • Therefore some Bs are Cs
- 36. Another example! • All As are Bs A B
- 37. Another example! • Some As are Cs A B C
- 38. Another example! • Therefore some Bs are Cs A B C The syllogism is valid
- 39. Now your turn Using Venn diagrams in your notebooks, decide whether each of the following arguments is valid or invalid.
- 40. Valid or invalid • All Bruneians eat durian • Kevin eats durian • Therefore Kevin is Bruneian
- 41. Valid or invalid • All Year 12 boys are brave • Some brave people are compassionate • Some Year 12 boys are compassionate
- 42. Valid or invalid • Some physicists are frauds • Some frauds are not wealthy • Therefore some physicists are not wealthy
- 43. Valid or invalid • All Chinese own dogs • No good football players have dogs • Therefore no Chinese are good football players
- 44. Valid or invalid • All clever girls are red-headed • All red heads are rich • Therefore all clever girls are rich
- 45. Inductive reasoning • All human beings are mortal This statement cannot be proved by logic and reasoning, but is based on experience. This brings us to inductive reasoning
- 46. Inductive reasoning Whilst deductive reasoning goes from the general to the particular, Inductive Reasoning goes from the particular to the general Going from “all observed human beings have died” to “all human beings are mortal” is an example of inductive reasoning
- 47. Inductive reasoning and generalisations Since inductive reasoning goes from the observed to the unobserved, it enables us to make generalisations about the world • All metals expand • All human beings are mortal
- 48. Generalisations Is there a danger to generalisations? Here is a list of 12 generalisations. Put them in order from the most reliable to the least reliable? (you may be asked to justify your order) 1. French people are rude. 2. Water boils at 100 °C. 3. Most graffiti artists are under 25 years old. 4. All generalisations are dangerous. 5. When spelling in English “i before e except after c”. 6. Dogs eat their own poo. 7. New Zealanders are good at rugby. 8. Year 12 students are lazy. 9. Metals expand when heated. 10. Chinese students are smarter. 11. Boys are better at physics than girls. 12. No-one succeeds without hard work.
- 49. Inductive reasoning What makes a good generalisation? You’ve got 5 minutes in your groups to think of “Five rules for making good generalisations”. When you’ve agreed your five rules can you write them in your books?
- 50. Inductive reasoning What makes a good generalisation? 1. Number: You should look at a good number of examples. If you see one dog swimming, this is not enough to decide that “all dogs can swim 2. Variety: You should look at a variety of circumstances. In the example of dogs swimming, looking at different breeds of dog. 3. Exceptions: You should actively look for counter examples. Look for dogs that can’t swim! 4. Coherence: You should look for more evidence to support surprising claims! If somebody suggests that dogs can swim because they have superpowers you may demand greater proof! 5) Subject area: Generalisations may be more reliable in some subject areas (e.g. science) than in others (e.g. economics or other social sciences).
- 51. Inductive turkeys 1. Some ‘inductive turkeys’ arrive on a farm one January. They are well looked after, and every morning after breakfast the farmer comes and feeds them. 2. After a few weeks, some of the more philosophical turkeys begin to notice that ‘when the farmer appears we get fed’. 3. As good inductive turkeys they continue to observe patiently, and as January turns to February the become increasingly confident of the truth of the generalisation that ‘whenever the farmer comes, we will get fed’. 4. The months pass, and as the spring turns to summer and as summer turns to autumn, this generalisation acquires the status of a law of nature. 5. The connection between the farmer’s appearance and the arrival of food, is the turkeys decide, a brute fact of reality, and to question it would be a clear sign of insanity. 6. Things continue in much the same way until one cold December morning – 24th December to be precise – 7. The farmer breaks the neck of the first Turkey that comes to him to be fed.
- 52. Activity 1. To what extent do human beings sometimes act like the turkeys in the story? 2. The turkeys turned out to be wrong, but do you think that their belief was reasonable? What does this suggest to you about the relationship between reason and truth? 3. When your dog gets excited when he sees you getting his lead out, do you think he is using inductive reasoning to predict you are going to take him for a walk?
- 53. The point • The story of the turkeys alerts us to the fact that even well confirmed generalisations can fail us. • Newton’s laws of motion were confirmed by observational evidence on countless occasions and were believed to be true for more than 200 years. Nevertheless they eventually turned out to be false. • Despite the obvious survival value of inductive reasoning we might ask how we can know that the future will be similar to the past in any respect. • How can we be sure that the laws of physics, together with the countless regularities that we take for granted, won’t suddenly break down tomorrow. • Think about the film The Matrix
- 54. Language and reasoning 1. Day and night? Where does night end and day begin? 2. Young or old? Is Mr Free young or old? Careful! 3. Grass is green? (Is it? Can you have non-green grass? 4. Man or woman? Is it that easy? 5. Pluto. Planet?
- 56. Discuss! The more churches there are in a city, the more prostitutes there are. Post hoc ergo propter hoc (Informal reasoning) Note: This is a TRUE statement. Bigger cities have more of everything – schools, McDonalds, hospitals, churches etc. Post hoc ergo propter hoc Assuming one thing causes another just because one follows another.
- 57. Discuss! People who have a tattoo are more likely to develop lung cancer. Note: This is true. Post hoc ergo propter hoc (Informal reasoning)
- 58. Chris says that he knows someone who is 90 and who has smoked 40 cigarettes a day for 75 years and he’s OK, so smoking can’t be harmful. Post hoc ergo propter hoc (Informal reasoning)
- 59. Kate bought a good luck charm and she seems to be doing better at school. Post hoc ergo propter hoc (Informal reasoning)
- 60. A summary of common fallacies 1. Ad ignorantiam: Claiming that something is true because it cannot be proved to be false. “Nobody has proved the Loch Ness Monster doesn’t exist” 2. Hasty generalisation: Generalising from insufficient evidence. 3. Ad hominem: Attacking /supporting the person rather than the argument. 4. Circular reasoning: Assuming the truth of what you are supposed to be proving.
- 61. A summary of common fallacies 5. Special pleading Using double standards to excuse an individual or group. 6. Equivocation Using language ambiguously. 7. False analogy Assuming that because two things are alike in one way that they are also alike in other ways. 8. False dilemma Assuming that only a limited number of alternatives exist. 9. Loaded question A question that is biased because it contains a built-in assumption.
- 62. post hoc ergo propter hoc Since strict gun control laws were introduced in Dodge City, the crime rate has risen. This shows that gun control does nothing to reduce crime. Decide which best applies to the argument. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question.
- 63. circular reasoning Roger Rabbit said he trusted me, and he must be telling the truth Because he wouldn’t lie to someone that he trusted. Decide which best applies to the argument. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question.
- 64. Decide which best applies to the argument. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. The ends justifies the means. After all, if you want to make omelettes, you have to break eggs. false analogy
- 65. Decide which best applies to the argument. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. ad hominem That can’t be right, non of my friends would believe it.
- 66. Decide which best applies to the argument. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. ad hominem Since many great scientists have believed in God, there must be some truth in religion.
- 67. hasty generalisation Claire and David got on very well on their two dates together. They are clearly well suited and should get married. Decide which best applies to the argument. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question.
- 68. Decide which best applies to the argument. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. false dilemma Do you want to be part of the solution, or part of the problem?
- 69. Decide which best applies to the argument. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. special pleading “I agree that you shouldn’t copy mp3s illegally, but I’ve only copied a few and I do buy tracks sometimes.”
- 70. Decide which best applies to the argument. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. equivocation The average UK family has 2.5 children. The Smiths are average people, they must have 2.5 kids.
- 71. Decide which best applies to the argument. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. ad ignorantium Since no-one has been able to prove that God didn’t create the universe, We must conclude that God did make everything.
- 72. Decide which best applies to the argument. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. loaded question Are all your family stupid, or is it just you?
- 73. Decide which best applies to the argument. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. ad ignorantium No scandal has ever touched Mr Free. He must be a clean living and honest man.
- 74. Decide which best applies to the argument. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. Just as you are more likely to take care of a car that you own rather than a car that you rent, A slave owner would look after a slave better than an employer would look after their worker. false analogy
- 75. ad ignorantium To ignore the possibility that Brunei landed the first person on the moon just because nobody has heard of a Bruneian space program is arrogant. If we are unaware of something does not mean that it never happened. Decide which best applies to the argument. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question.
- 76. Decide which best applies to the argument. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. false dilemma In the fight against terrorism, you are either with the USA or against.
- 77. What do you think? • In most legal systems, someone who is accused of a crime is considered innocent until proven guilty. • Is this an example of argument ad ignorantiam? • Should we abandon this assumption?
- 78. Causes of bad reasoning • Rationalisation – Manufacturing arguments to justify our ignorance, pride, laziness and prejudices • Take any editorial or opinion article from a newspaper and see how many logical fallacies you can find in it. • Have you ever rationalized?
- 79. Bad Reasoning • Ignorance – we are taken aback when we realise a particular form of reasoning is fallacious. • Laziness – we have fixed habits of thinking or are too lazy to check the arguments or the evidence. Simple beliefs are easier.
- 80. Bad Reasoning • Pride – we may be open-minded but sometimes winning the argument is more important than the truth. Logic gives way to Rhetoric. Prejudice – We can even begin with prejudices and manufacture bad reasons to justify them – Rationalisation.
- 81. “Thinking out the box” Lateral Thinking • Both inductive and deductive reasoning have their flaws and often confine the knower to a systematic approach to thinking. • So perhaps it is better if we all had a little more intellectual flexibility. • According to Eduardo de Bono (1993-) if we are to escape from the ‘prison of consistency’ then we must learn to ‘think outside of the box’ and come up with more creative ways to looking at problems. • He argues we cannot rely on traditional logic to give us new ideas, we need to adopt a more creative way of thinking that encourages us to search actively for better solutions to problems.
- 82. Top Floor A man lives in the penthouse of an apartment building. Every morning he takes the elevator down to the lobby and leaves the building. Upon his return, however, if he is alone he can only travel halfway up in the lift and has to walk the rest of the way - unless it's raining. What is the explanation for this? He’s a dwarf and cannot press the top buttons in the elevator (unless it is raining when he uses an umbrella).
- 83. Falling Baby How could a baby fall out of a twenty-story building onto the ground and live? The baby fell out of a ground floor window.
- 84. Hands up! • Assume there are approximately 6 billion people on Earth. • What would you estimate to be the result, if you multiply together the number of fingers on every person's left-hands? Zero. It only takes one person to have no fingers on their left hand for the product to be zero, because anything multiplied by zero equals zero.
- 85. Baby puzzle • A woman gave natural birth to two sons who were born on the same hour of the same day of the same month of the same year. • But they were not twins and she had no access to a time machine. • How could this be? They were two babies from a set of triplets
- 86. Conclusion • Rationalist philosophers like Rene Descartes believed that reason was a way of knowing that can give us certainty. • However, reason is only as certain as the premises on which it is based, and it is also possible that we have reasoned badly in arguing from premises to conclusions. • While there are limitations to both induction and deduction, in practice it is difficult to see how we can do without these two ways of reasoning. • Reason like other ways of knowing is a double edged tool. • We need to reason to develop consistent beliefs about the world but we can become trapped in the ‘prison of logic’ and this can stifle our creativity. • Furthermore, reason is not appropriate in every situation, and if someone is too rational they may simply come across as a cold and unfeeling robot. • Reason needs to be balanced by emotion. YouTube - Argument Clinic
- 87. Let’s write another essay! • Is adversarial argument the best way to decide someone’s innocence. Discuss.
- 88. Problems with Inductive Reasoning 1. Ad ignorantiam: Claiming that something is true because it cannot be proved to be false. 2. Hasty generalisation: Generalising from insufficient evidence. 3. Ad hominem: Attacking /supporting the person rather than the argument. 4. Circular reasoning: Assuming the truth of what you are supposed to be proving. 5. Special pleading Using double standards to excuse an individual or group. 6. Equivocation Using language ambiguously. 7. False analogy Assuming that because two things are alike in one way that they are also alike in other ways. 8. False dilemma Assuming that only a limited number of alternatives exist. 9. Loaded question A question that is biased because it contains a built-in assumption Handout: Inductive reasoning What makes a good generalisation? 1. Number: You should look at a good number of examples. If you see one dog swimming, this is not enough to decide that “all dogs can swim 2. Variety: You should look at a variety of circumstances. In the example of dogs swimming, looking at different breeds of dog. 3. Exceptions: You should actively look for counter examples. Look for dogs that can’t swim! 4. Coherence: You should look for more evidence to support surprising claims! If somebody suggests that dogs can swim because they have superpowers you may demand greater proof! 5) Subject area: Generalisations may be more reliable in some subject areas (e.g. science) than in others (e.g. economics or other social sciences).