Argument and Analysis

1. Argument and Analysis

2. Arguments • An argument is a set of claims put forward as reasons to believe some statement.

3. Arguments • An argument is a set of claims put forward as reasons to believe some statement. • The reasons are given in the premisses • The statement they support is the conclusion

4. Arguments • An argument is a set of claims put forward as reasons to believe some statement. • The reasons are given in the premisses • The statement they support is the conclusion An argument If children like ice-cream, and Bob is a child, then Bob likes ice-cream

5. Arguments • An argument is a set of claims put forward as reasons to believe some statement. • The reasons are given in the premisses • The statement they support is the conclusion An argument in standard form P1 Children like ice-cream P2 Bob is a child C Bob likes ice-cream

6. Arguments • Two kinds of arguments • Deductive - conclusion doesn’t tell us more about the world than the premisses

7. Arguments • Two kinds of arguments • Deductive - conclusion doesn’t tell us more about the world than the premisses • Inductive – does claim to tell us more

8. Arguments • Two kinds of arguments • Deductive - conclusion doesn’t tell us more about the world than the premisses • If children like ice-cream, and Bob is a child, then Bob likes ice-cream • Inductive – does claim to tell us more

9. Arguments • Two kinds of arguments • Deductive - conclusion doesn’t tell us more about the world than the premisses • If children like ice-cream, and Bob is a child, then Bob likes ice-cream • Inductive – does claim to tell us more • All the swans I have seen are black. Therefore all swans are black

10. Deductive Arguments • Validity • If the premisses are true then the conclusion must be true • Note: if the premisses are false then the conclusion may be false

11. Deductive Arguments • Validity • If the premisses are true then the conclusion must be true • Note: if the premisses are false then the conclusion may be false • Soundness • The argument is valid and the premisses are true • Note: the conclusion must be true

12. Deductive Arguments • Logic • Some arguments are valid just because of their form All men are mortal Socrates is a man Socrates is mortal

13. Deductive Arguments • Logic • Some arguments are valid just because of their form All men are mortal All A are B Socrates is a manC is an A Socrates is mortal C is B

14. Deductive Arguments • Not Logic • Some arguments are not valid just because of their form Socrates is a bachelor Socrates is unmarried.

15. Deductive Arguments • Not Logic • Some arguments are not valid just because of their form Socrates is a bachelorA is a B Socrates is unmarried A is C

16. Deductive Arguments • Disproving Validity • Method 1 — The Counterexample Method

17. Deductive Arguments • Disproving Validity • Method 1 — The Counterexample Method • Determine the pattern of the argument to be criticised

18. Deductive Arguments • Disproving Validity • Method 1 — The Counterexample Method • Determine the pattern of the argument to be criticised • Construct a new argument with: (a) the same pattern (b) obviously true premises; and (c) an obviously false conclusion.

19. Deductive Arguments • Disproving Validity • Method 1 — The Counterexample Method Example If God created the universe then the theory of evolution is wrong The theory of evolution is wrong God created the universe

20. Deductive Arguments • Disproving Validity • Method 1 — The Counterexample Method Example If A then B B A

21. Deductive Arguments • Disproving Validity • Method 1 — The Counterexample Method Example If Stephen is a wombat then Stephen is a mammal T Stephen is a mammal T Stephen is a wombat F !

22. Deductive Arguments • Disproving Validity • Method 2 — Invalidating Possible Situations

23. Deductive Arguments • Disproving Validity • Method 2 — Invalidating Possible Situations Describe a possible situation in which the premises are obviously true and the conclusion is obviously false

24. Deductive Arguments • Disproving Validity • Method 2 — Invalidating Possible Situations Example (Fallacy of Affirming the Consequent) If my car is out of fuel it won’t start My car won’t start My car is out of fuel

25. Deductive Arguments • Disproving Validity • Method 2 — Invalidating Possible Situations Example (Fallacy of Affirming the Consequent) My car will indeed not start without fuel (it is a fuel-driven car) and the electrical system needed to start the car has been taken out for repairs (so it won't start). Yet the car has a full tank of petrol.

26. Deductive Arguments • Disproving Validity • Method 2 — Invalidating Possible Situations Example (Fallacy of Denying the Antecedent) If the committee addresses wilderness values it must address naturalness It will not address wilderness values It need not address naturalness

27. Deductive Arguments • Disproving Validity • Method 2 — Invalidating Possible Situations Example (Fallacy of Denying the Antecedent) Wilderness value involves, amongst other things, naturalness (Federal legislation actually defines 'wilderness value' this way). Moreover, the Committee's terms of reference do not include consideration of wilderness value (so it won't address it). Yet the Committee is explicitly formed to consider naturalness (to feed their findings into those of other Committees, so that a joint finding can be made regarding wilderness values)

28. Deductive Arguments • Fallacies • Are errors which look a lot like valid arguments

29. Deductive Arguments • Fallacies • Are errors which look a lot like valid arguments Example (Fallacy of Affirming the Consequent) Form: If P then Q Q P

30. Deductive Arguments • Fallacies • Are errors which look a lot like valid arguments Example (Fallacy of Affirming the Consequent) Form: Resembles: If P then Q If P then Q Q P P Q (Modus Ponens)

31. Deductive Arguments • Fallacies • Are errors which look a lot like valid arguments Example (Fallacy of Denying the Antecedent) Form: If P then Q ~P ~Q

32. Deductive Arguments • Fallacies • Are errors which look a lot like valid arguments Example (Fallacy of Denying the Antecedent) Form: Resembles: If P then Q If P then Q ~P ~Q ~Q ~P (Modus Tollens)

33. Inductive Arguments • Two kinds • Argument from Analogy • Inference to Best Explanation

34. Inductive Arguments • Argument from Analogy Consider a watch. A watch exhibits (a) complexity of parts; (b) suitability to fulfil a certain function (i.e. telling the time); and (c) its complexity is what enables it to fulfil this function. These three features are extremely unlikely to have come about by accident. No one on seeing a watch would think it the product of chance. Even seeing it for the first time, one would conclude that it is the product of design by some intelligent being. But many things in nature we observe (e.g. the eye) are similarly complex, fulfil a function (e.g. seeing) and their complexity enables them to fulfil this function. So it is reasonable to suppose that they too are made by an intelligent being

35. Inductive Arguments • Argument from Analogy P1 A watch has (a), (b), (c). P2 The world has (a), (b), (c). P3 Watches require a watch-maker C The world requires a world-maker

36. Inductive Arguments • Argument from Analogy P1 The Object has properties P1,P2,…,Pn P2 The Analogue also has P1,P2,…,Pn P3 The analogue has property P C Therefore the object has property P

37. Inductive Arguments • Argument from Analogy (as a deduction) P1 The Object has properties P1,P2,…,Pn P2 The Analogue also has P1,P2,…,Pn P3 The analogue has property P P4* If A & B share P1,P2,…,Pn they share P C Therefore the object has property P

38. Inductive Arguments • Evaluating Arguments from Analogy • Are the premisses true?

39. Inductive Arguments • Evaluating Arguments from Analogy • Are the premisses true? • Is the analogy strong?

40. Inductive Arguments • Evaluating Arguments from Analogy • Are the premisses true? • Is the analogy strong? • Are P1,P2,…,Pn relevant to P?

41. Inductive Arguments • Evaluating Arguments from Analogy • Are the premisses true? • Is the analogy strong? • Are P1,P2,…,Pn relevant to P? • Are there disanalogies?

42. Inductive Arguments • Evaluating Arguments from Analogy • Are the premisses true? • Is the analogy strong? • Are P1,P2,…,Pn relevant to P? • Are there disanalogies? • Is the conclusion too strong?

43. Inductive Arguments • Inference to Best Explanation You return home to find your door broken and some valuable items missing. This cries out for explanation. Possible explanations include: (1)A meteorite struck your door and vaporised your valuables, (2) friends are playing a joke on you, (3) a police Tactical Response Group entered your house mistakenly, and (4) you were robbed. Explanation 4 seems the best, so you conclude you were robbed.

44. Inductive Arguments • Inference to Best Explanation P1 Phenomenon A is observed P2 Explanation X explains A and does so better than any rival explanation C X is the case

45. Inductive Arguments • Evaluating Inference to Best Explanation • Is there anything that needs explaining?

46. Inductive Arguments • Evaluating Inference to Best Explanation • Is there anything that needs explaining? • What is the ‘best’ explanation? • Evaluate for Strength

47. Inductive Arguments • Evaluating Inference to Best Explanation • Is there anything that needs explaining? • What is the ‘best’ explanation? • Evaluate for Strength • Does it really explain?

48. Inductive Arguments • Evaluating Inference to Best Explanation • Is there anything that needs explaining? • What is the ‘best’ explanation? • Evaluate for Strength • Does it really explain? • Is it more widely applicable?

49. Inductive Arguments • Evaluating Inference to Best Explanation • Is there anything that needs explaining? • What is the ‘best’ explanation? • Evaluate for Strength • Does it really explain? • Is it more widely applicable? • Is it as simple as possible?

50. Inductive Arguments • Evaluating Inference to Best Explanation • Is there anything that needs explaining? • What is the ‘best’ explanation? • Evaluate for Strength • Does it really explain? • Is it more widely applicable? • Is it as simple as possible? • Is it conservative of prior beliefs?