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  1. Rationalism the use of reason

  2. Deductive and Inductive Logic Deductive Logic involves cases where, given some information, the conclusion must be true. Eg • All humans are mortal. • I am human • Therefore I am mortalOr: • 6x + 7y = z • x=2, y=3 • Therefore, z=33

  3. Deductive and Inductive Logic Inductive Logic does not involve certainty in the same way, in inductive logic we must go on what we have always experienced to be the case before. • Day has always followed night, so I assume that after tonight there will be another day. • Mr Appleton never tells me off when I don't do my homework for him, so I won't bother doing my homework for him today.

  4. Paradigms A paradigm is a set of beliefs or expectations that we have about the world. Paradigms shape our interpretation of what we perceive.

  5. Justify the following beliefs… • a) Imagine you lived in the time when people believed the Earth was flat. • b) Imagine you lived in the time when people believed the earth was the center of the universe. • c) Imagine you lived in a time when people believed slavery was justifiable.

  6. Induction and the Scientific method • Induction is the main scientific method; and scientists have to be constantly aware that the latest theory is simply a best fit model. • If a theory works today, and it has worked every time before, then it is the best theory for the time; but it may change (as in the earlier paradigm shifts.)

  7. The PROBLEM of Induction • Induction is about the human need to look for patterns in the chaos (like science!!). • But we need to be careful…… • Don’t let our need to categorize and classify lead us to seeing what isn’t really there!

  8. All students are lazy: • I am a student. • Therefore I am lazy. False True False

  9. Truth and Validity • You can see that this is a perfectly valid logical argument. If A and B are true then C must be true. However the conclusion is obviously dubious because at least one of the premises of the argument (A or B) is incorrect (that is, it is not true that all students are lazy). There are two completely separate issues here - the truth of the premises themselves and the correctness of the method used to draw a conclusion from the premises (the logical argument). This is an extremely important point. • For the conclusion of a logical argument to be true, the logic must be correctand the premises must be true. If you want to undermine an argument, you can try to fault the logic or you can dispute the premises of the argument. This is what lawyers do!!

  10. Janice is a biologist. She reasons: • All pelicans like to eat fish. • I like to eat fish. • Conclusion: I am a pelican. True True False

  11. All TOK teachers wear glasses; • Mr Appleton is a TOK teacher; • Therefore Mr Appleton wears glasses.

  12. All people in the classroom at the moment are at school. • I am in the classroom at the moment; • Therefore I am at school.

  13. All terrorists commit acts of violence. • This man has committed an act of violence. • Therefore this man is a terrorist.

  14. Most people in England speak English. • Most people in New Zealand speak English. • Therefore most people in China speak English.

  15. Violent people like watching violent movies. • Bill likes watching violent movies. • Therefore Bill is a violent person

  16. All enemies of democracy criticise western governments; • Mr Hinchliffe criticizes western governments. • Therefore Mr Hinchliffe is an enemy of democracy.

  17. The PROBLEM of Induction • Induction is about the human need to look for patterns in the chaos (like science!!). • But we need to be careful…… • Don’t let our need to categorise and classify lead us to seeing what isn’t really there!

  18. All Australian cities are in the southern hemisphere. • Sydney is not an Australian city. • Therefore: Sydney is not in the southern hemisphere.

  19. All American states have beaches. • Hawaii is an American state. • Therefore: Hawaii has beaches.

  20. All Australian states are in the southern hemisphere. • Queensland is an Australian state. • therefore: Queensland is in the southern hemisphere.

  21. All politicians are exceptionally honest people. • I am a politician. • Therefore: I am an exceptionally honest person.

  22. Most people in England speak English. • Most people in New Zealand speak English. • therefore: Most people in China speak English.

  23. Helen is well off. She is asked to give some money to a charity for poor people in her town. • She reasons: I know it is my duty to help people in need There are many poor people in this town. If I give away almost all my money, I can help all of them become a little better off, as well off, in fact, as I will then be. • Conclusion: I will give almost all my money to the poor.

  24. Adam is a concentrationcamp guard. His superior officer tells him to shoot a woman who has been protesting. • He reasons: He is my superior officer and I am under his command. If he gives an order, then it is my duty to obey. I feel awful about the woman, but logically I should ignore my emotions and do my duty. • Conclusion: I should shoot the woman.

  25. Prue finds herself in a position where she must trust one of two strangers, Sue and Tess. • She reasons: I have no logical reason for trusting one rather than the other. I have a better feeling about Sue than about Tess, but a feeling is no good reason for acting. • Conclusion: I will flip a coin to decide.

  26. Eric is a worker in a factory. He sees the boss being very unpleasant to a young fellow worker. • He reasons: The way the boss treated that worker makes me really angry. If I complain to the union, they will be able to have the boss restrained from such behaviour. • Conclusion: I will complain to the union.

  27. Ivan is well off and has a young family who he loves. He is asked to give some money to a charity for poor people in his town. • He reasons: I know it is my duty to help people in need. There are many poor people in this town. If I give away almost all my money, I can help all of them become a little better off - as well off, in fact, as I and my family will then be. • Conclusion: Even though my children will grow up in near poverty, I will give almost all my money to the poor.

  28. Olivia finds herself in a position where she must trust one of two strangers, Sue and Tess. • She reasons: I have no logical reason for trusting one rather than the other. However, I have a better feeling about Sue than about Tess. • Conclusion: I will trust Sue.

  29. Neville is in a music club, jamming with some other musicians. He plays a difficult tune well. • He reasons: Playing well makes you feel happy. I have just played well and I feel really happy now. • Conclusion: I will play a lot more music so that I will feel even happier.

  30. Gerry is well off. He is asked to give some money to a charity for poor people in his town. • He reasons: It gives me great pleasure to be nice to other people and see them a little better off. • Conclusion: I will give money to the poor.

  31. The Real World….. • Do we really go through such a logical thought process when we make decisions in our lives? Discuss some major decisions you have had to make and look at the reasoning process you went through. Perhaps you used some induction and some deduction, but there will have been other things at play... emotion, instinctive feelings, faith, authority. • Discuss these things with your partner.

  32. Truth of Conclusions Danger in interpretation

  33. Incident in the Store • The old man had just turned off the lights in the store and was preparing to lock up and go home when a youth appeared and demanded money. The owner opened the cash register; the contents were grabbed, and the man ran away. The police were informed immediately.

  34. A young man appeared after the lights had been turned off. The old man was preparing to go home. The robber demanded money. Someone opened the cash register. The robber demanded money from the owner. The person who opened the cash register was a man. The cash register contained money, but we are not told howmuch money. The gender of the owner was not revealed in the story.' The robber did not demand money. After the man grabbed the contents of the cash' register, he ran away. The young man appeared after the lights had been turned off. The robber was a man. The owner was a man. The owner appeared and demanded money. The man ran away after he had demanded money Incident in the Store – what happened?

  35. The dangers of crossing the road The old lady had just finished her shopping and was starting to cross the road when a car sped around the corner. The cyclist, fearing an accident, shouted 'Watch out', and the car driver slammed on the brakes - but it was too late. A collision was unavoidable. Shopping bags were scattered all over the road, but fortunately no-one was seriously injured. The police appeared soon afterwards and interviewed all the relevant witnesses. The lady's poor vision had contributed to the accident and the car had been speeding.

  36. There was a car traveling faster than the speed limit. The old lady in the story had been shopping. A vehicle came round the corner just after a lady had stepped off the pavement. The car driver was unable to avoid a collision. The police came to investigate the incident. Although the old lady was struck by the car, she was not seriously injured. Shopping was scattered over the road. The driver slammed on his brakes. The police interviewed the car driver. The old lady had poor eyesight. The car's speeding contributed to the accident. The old lady was riding a bicycle. The cyclist was seriously injured. There was at least one car driver involved in the accident. The lady crossed the road near a corner. Road Accident – what happened?

  37. Truth and validity • As a matter of fact, it seems that humans find it very difficult indeed to make deductions strictly on the basis of evidence. Instead, we seem to tell ourselves a story, to make assumptions and to embroider events according to our own personal prejudices.

  38. Arguments, Axioms and Assumptions • Look at the arguments on the worksheet. • How compelling is the articulate use of speech? • How do politicians and advertisements use this skill?

  39. What assumptions are unstated in the following? • Property prices are bound to drop soon since they have been rising for a long time now. • It must be a good school - the fees are so high. • I'm not doing maths homework today because I need to work on my history. • Female office workers work just as hard as male office workers and are just as productive. Therefore female office workers doing the same job as men should receive the same pay. • Marijuana should be legalised because it is no more dangerous than alcohol, and less dangerous than tobacco, both of which are already legal. • Marijuana should not be legalised because it leads to the use of harder drugs such as heroin.

  40. Distinction between validity and truth • Items 7-10 reinforce the crucial distinction between validity and truth. In particular, it is interesting to see that logic is of no help in choosing between arguments. This is perhaps rather surprising, especially since we were hoping to use reason as a tool in our search for truth and certainty. It seems not to be living up to our initial hopes

  41. 7 Welfare states • Welfare systems discourage people from working. Having lots of people unemployed is bad for the economy. Therefore, if we want a healthy economy we should look for ways to abandon the welfare system. • The more very poor people you have in a generally rich country, the higher the crime rate. A high level of welfare stops people from being very poor, so to keep crime low we should maintain this high level of welfare.

  42. 8 Racism • Minorities suffer from increasing racism in a certain country. An increase of foreigners will lead, in practice, to more people suffering from racism. Therefore existing minorities are actually helped by tough immigration laws. • Minorities suffer from increasing racism in a certain country. An increase of foreigners will, over time, lead to greater acceptance of all minorities. Therefore existing minorities are disadvantaged by tough immigration laws.

  43. 9 Abortion • Killing someone, unless in self-defence, is wrong. Abortion kills unborn babies. Therefore abortion is wrong. • What happens to a person's body is ultimately their decision. To prevent a person deciding about their own body is wrong. Having an abortion involves a woman deciding about her body, so to prevent her doing that would be wrong. Hence preventing abortion is wrong.

  44. 10 Superiority of Human Race • A race that places itself above all others is despicable. Humans place themselves above all other animals. Therefore humans are despicable. • A race that did not place itself above all others would not have survived for very long. Hence placing one's race above all others is a natural survival trait. Hence it is perfectly, acceptable to place one's race above all others

  45. What we need to know… • understand that the use of reason is a way to extend our knowledge from known facts • be able to distinguish between inductive and deductive arguments - in both cases to evaluate the strengths and weaknesses of the arguments • understand the premises/conclusion nature of an argument: • be very clear about the relationship between a valid argument and a true conclusion • be aware of the need to be rigorous when using logic, the difficulties associated with choice of premises, the dangers of hidden assumptions and the problems with definitions • be familiar with some elementary fallacies • be able to apply these ideas to everyday examples • appreciate that real-life problem solving requires imagination and creativity, and more than simple logic