1. Logic & Critical Thinking @ Herman J. SuhendraProduced by Herman J. Suhendra A.B. Gadjah Mada University & M.A. University of Santo Tomas, Manila MEETING 5 Argument Part 2

3. Arguments - Part 1 (of 3) 1. Distinguishing Fact & Opinion 7. Evaluating Arguments 2. What is an Argument? 5. Deduction & Induction 6. Analyzing Arguments 8. Writing Arguments 3. Identifying Premises & Conclusions 4. What Is Not an Argument?

5. Remember! Before we can effectively analyze and evaluate an argument, we need to understand clearly what kind of argument is being offered.

6. Deduction & Induction Arguments below deductive or inductive? Argument 1 All Humans are Mortal. SBY is human. Therefore, SBY is Mortal. Argument 2 All of Steven Spielberg‘s movies have been good. Therefore, Steven Spielberg‘s next movie will probably be good. Types of Arguments: Deductive arguments Deductive arguments are arguments in which the conclusion is claimed or intended to follow necessarily from the premises. Inductive arguments Inductive arguments are arguments in which the conclusion is claimed or intended to follow probably from the premises.

7. Key Differences: Deductive arguments claim that… Inductive arguments claim that…  If the premises are true, then the conclusion must be true.  The conclusion follows necessarily from the premises.  The premises provide conclusive evidence for the truth of the conclusion.  It is impossible for all the premises to be true and the conclusion false.  It is logically inconsistent to assert the premises and deny the conclusion, meaning that if you accept the premises, you must accept the conclusion.  If the premises are true, then the conclusion is probably true.  The conclusion follows probably from the premises.  The premises provide good (but not conclusive) evidence for the truth of the conclusion.  It is unlikely for the premises to be true and the conclusion false.  Although it is logically consistent to assert the premises and deny the conclusion, the conclusion is probably true if the premises are true.

8. Deduction & Induction There are four tests that can be used to determine whether an argument is deductive or inductive: 1.The Indicator Word Test 2.The Strict Necessity Test 3.The Common Pattern Test 4.The Principle of Charity Test

9. 1. The Indicator Word Test indicator word test The indicator word test asks whether there are any indicator words that provide clues whether a deductive or inductive argument is being offered. Common deduction indicator words include words or phrases like necessarily, logically, it must be the case that, and this proves that. Common induction indicator words include words or phrases like probably, likely, it is plausible to suppose that, it is reasonable to think that, and it's a good bet that. In the example above, the word probably shows that the argument is inductive. Femina is a PU student. Most PU students own laptops. So, probably Femina owns a laptop.

10. The Mona Lisa, by Da Vinci, is an excellent piece of art. The Last Supper, by Da Vinci, is an excellent piece of art. The Madonna of the Rocks, by Da Vinci, is an excellent piece of art. So probably, all works done by Da Vinci are excellent pieces of art. deductive or inductive? Why?

11. 2. The Strict Necessity Test strict necessity test The strict necessity test asks whether the conclusion follows from the premises with strict logical necessity. If it does, then the argument is deductive. In this example, the conclusion does follow from the premises with strict logical necessity. Although the premises are both false, the conclusion does follow logically from the premises, because if the premises were true, then the conclusion would be true as well. Taxis are architects. No architects are Democrats. So, no Taxis are Democrats.

12. Our national heroes are Javanese. Pangeran Diponegoro is a national hero. Therefore, Pangeran Diponegoro is a Javanese. deductive or inductive? Why?

13. 3. The Common Pattern Test common pattern test The common pattern test asks whether the argument exhibits a pattern of reasoning that is characteristically deductive or inductive. If the argument exhibits a pattern of reasoning that is characteristically deductive, then the argument is probably deductive. If the argument exhibits a pattern of reasoning that is characteristically inductive, then the argument is probably inductive. In the example above, the argument exhibits a pattern of reasoning called "argument by elimination.“ Arguments by elimination Arguments by elimination are arguments that seek to logically rule out various possibilities until only a single possibility remains. Arguments of this type are always deductive. Either Djoko voted in the last election, or he didn't. Only citizens can vote. Djoko is not, and has never been, a citizen. So, Djoko didn't vote in the last election.

14. 4. The Principle of Charity Test principle of charity test In this passage, there are no clear indications whether Zeno's argument should be regarded as deductive or inductive. For arguments like these, we fall back on the principle of charity test. principle of charity test According to the principle of charity test, we should always interpret an unclear argument or passage as generously as possible. We could interpret Zeno's argument as deductive. But this would be uncharitable, since the conclusion clearly doesn't follow from the premises with strict logical necessity. (It is logically possible-- although highly unlikely--that a 90-year-old woman who walks with a cane could climb Gunung Merbabu.) Thus, the principle of charity test tells us to treat the argument as deductive. Ramlan: Karen told me her grandmother recently climbed Gunung Merbabu. Zeno : Well, Karen must be pulling your leg. Karen's grandmother is over 90 years old and walks with a cane.

15. 80% of the Indonesian lives below the poverty line. Martono is an Indonesian. So probably, Martono lives below the poverty line. deductive or inductive? Why?

16. If Munir was assassinated, then he died. He was assassinated. Therefore, he died. deductive or inductive? Why?

17. Exercise 1 Tony: Are there any good Italian restaurants in town? Nasir: Yeah, Luigi's is pretty good. I've had their Neapolitan rigatoni, their lasagne col pesto, and their mushroom ravioli. I don't think their lasagne col pesto, and their mushroom ravioli. I don't think you can go wrong with any of their pasta dishes. you can go wrong with any of their pasta dishes. Is Nasir’s argument deductive or inductive? Why?

18. Exercise 2 Is this argument deductive or inductive? Why? I wonder if I have enough cash to buy my journalism textbook as well as my public relations and communication textbooks. Let's see, I have Rp200.000. My journalism textbook costs Rp65.000 and my communication textbook costs Rp52.000. My public relations textbook costs Rp60.000. With taxes, that should come to about Rp190.000 Yep, I have enough.

19. Exercise 3 deductive or inductive? Why? Mother: Don't give Jason that brownie. It contains walnuts, and I think he is allergic to walnuts. Last week he ate some oatmeal think he is allergic to walnuts. Last week he ate some oatmeal cookies with walnuts, and he broke out in a severe rash. Father: Jason isn't allergic to walnuts. Don't you remember he ate cookies with walnuts, and he broke out in a severe rash. Father: Jason isn't allergic to walnuts. Don't you remember he ate some walnut fudge ice cream at Ferrari's birthday party last some walnut fudge ice cream at Ferrari's birthday party last spring? He didn't have any allergic reaction then. spring? He didn't have any allergic reaction then.

20. Exercise 4 deductive or inductive? Why? I went to Burger King last night and the service was horrible. The same thing happened the last time I went there. The same thing happened the time before that. Hence the service at Burger King is always horrible.

21. Exercise 5 deductive or inductive? Why? Susan is under 18. People under 18 in Indonesian cannot vote. Therefore, Susan cannot vote

22. Exercise 6 deductive or inductive? Why? Imagine a friend gave you a guinea pig to look after but forgot to tell you anything about what to feed it. You might say to yourself, 'I have a guinea pig and do not know what to feed it; but I do know that my rabbit eats carrots, and that rabbits and guinea pigs are similar. Hence, I can probably feed my guinea pig carrots as well'.

23. Exercise 7 deductive or inductive? Why? Shaving cream is clearly similar in colour, texture, moistness, and body to whipped cream, and I know that whipped cream is delicious on fruit salad. Hence, shaving cream is delicious on fruit salad.

24. Deduction & Induction TypeDescriptionInductiveReasoning  Making observations, and then drawing conclusions from those observations  Moves from specific evidence to general conclusion  Conclusion must be figured out and then evaluated for validity  Inductive = Evidence  Conclusion  Questions to ask:  What evidence is available? What has been observed?  What can be concluded from that evidence?  Is that conclusion logical? DeductiveReasoning  Moves from conclusion to evidence for the conclusion  Evaluate if the evidence is valid  Includes formal logic  Deductive = Conclusion  Evidence  Questions to ask:  What is the conclusion?  What evidence supports it?  Is that evidence logical?

26. Deductive Validity Argument #1 : Barbie is over 90 years old. So Barbie is over 20 years old. Argument #2 : Barbie is over 20 years old. So Barbie is over 90 years old.

27. Deduction Validity Argument #1 : Barbie is over 90 years old. So Barbie is over 20 years old. Argument #2 : Barbie is over 20 years old. So Barbie is over 90 years old. Intuitively, the conclusion of the first argument follows from the premise, whereas the conclusion of the second argument does not follow from its premise. But how should we explain the difference between the two arguments more precisely? Here is a thought : In the first argument, if the premise is indeed true, then the conclusion cannot be false. On the other hand, even if the premise in the second argument is true, there is no guarantee that the conclusion must also be true. For example, Barbie could be 30 years old.

28. Deduction Validity Argument #1 : Barbie is over 90 years old. So Barbie is over 20 years old. Argument #2 : Barbie is over 20 years old. So Barbie is over 90 years old. Intuitively, the conclusion of the first argument follows from the premise, whereas the conclusion of the second argument does not follow from its premise. But how should we explain the difference between the two arguments more precisely? Here is a thought : In the first argument, if the premise is indeed true, then the conclusion cannot be false. On the other hand, even if the premise in the second argument is true, there is no guarantee that the conclusion must also be true. For example, Barbie could be 30 years old.

29. Deductive VALID (official definition) Iff It is impossible the conclusion to be FALSE while all the premises are true. That is : There is no logically possible situation where all the premises are true and the conclusion is false at the same time. VALID (intuitive idea) Iff the truth of premises 100% logically guarantees the truth of conclusion. It is logically NECESSARY that IF all the premises are true THEN the conclusion is also true. INVALID Iff it is not logically NECESSARY that IF all the premises are true THEN the conclusion is also true. Iff it is logically POSSIBLE for the conclusion to be false WHILE all the Premises are true.

30. What do we mean by “logically possible”? Anything is logically possible so long as it is NOT self-contradictory. IMPORTANT: “VALIDITY” is a logical concept: it is defined in terms of “logical possibilty”. (NOT any other kinds of possibility: Economy, political, technological, psychological, physical, or legal possibilities) POSSIBILITY: that which is ALLOWED (i.e. not ruled out) IMPOSSIBILITY: that which is ruled out (i.e. not allowed). SOMETHING is logically possible (or logically impossible): it is allowed (or ruled out) by the laws of LOGIC. LAW OF NON-CONTRADICTION: SELF-CONTRADICTION (i.e. “P and not-P”) IS NOT ALLOWED

31. Deductive The idea of validity provides a more precise explication of what it is for a conclusion to follow from the premises. Applying this definition, we can see that the FIRST argument above is VALID, since there is no possible situation where Barbie can be over 90 but not over 20. The SECOND argument is INVALID because there are plenty of possible situations where the premise is true but the conclusion is false. Consider a situation where Barbie is 25, or one where she is 85. The fact that these situations are possible is enough to show the argument is not VALID, or INVALID.

32. Deductive All pigs can fly. Anything that can fly can swim. So all pigs can swim.

33. Deductively Although the two premises of this argument are false, this is actually a VALID argument. To evaluate its validity, ask yourself whether it is possible to come up with a situation where all the premises are true and the conclusion is false. (We are not asking whether there is a situation where the premises and the conclusion are all true.) Of course, the answer is 'no'. If pigs can indeed fly, and if anything that can fly can also swim, then it must be the case that all pigs can swim. So this example tells us something: (1) The premises and the conclusion of a valid argument can all be false.

34. Deductive Hopefully you will now realize that validity is not about the actual truth or falsity of the premises or the conclusion. Validity is about the logical connection between the premises and the conclusion. A valid argument is one where the truth of the premises guarantees the truth of the conclusion, but validity does not guarantee that the premises are in fact true. All that validity tells us is that if the premises are true, the conclusion must also be true.

35. Deductive Adam loves Beth. Beth loves Cathy. So Adam loves Cathy.

36. Deductive

37. Deductive Invalid for it is possible that the premises are true and yet the conclusion is false. Perhaps Adam loves Beth but does not want Beth to love anyone else. So Adam actually hates Cathy. The mere possibility of such a situation is enough to show that the argument is not valid. Let us call these situations invalidating counterexamples to the argument. Basically, we are defining a valid argument as an argument with no possible invalidating counterexamples. Note: to sharpen your skills in evaluating arguments, it is therefore important that you are able to discover and construct such examples.

38. Deductive Notice that a counterexample need not be real in the sense of being an actual situation. It might turn out that in fact that Adam, Beth and Cathy are members of the same family and they love each other. But the above argument is still invalid since the counterexample constructed is a possible situation, even if it is not actually real. All that is required of a counterexample is that the situation is a coherent one in which all the premises of the argument are true and the conclusion is false. So we should remember this : (2) An argument can be invalid even if the conclusion & the premises are all actually true.

39. Deductive All pigs are purple in colour. Anything that is purple is an animal. So all pig are animals.

40. Deductive (3) It is possible for a VALID argument to have a true conclusion even. when all its premises are false.

41. Deductive The concept of validity provides a more precise explication of what it is for a conclusion to follow from the premises. Since this is one of the most important concepts, you should make sure you fully understand the definition. In giving our definition we are making a distinction between truth and validity. In ordinary usage "valid" is often used interchangeably with "true" (similarly with "false" and "not valid"). But here validity is restricted to only arguments and not statements, and truth is a property of statements but not arguments: So never say things like “this statement is valid” or “that argument is true”!

42. Exercise 2 Someone is sick. Someone is unhappy. So, Someone is unhappy and sick. Valid or Invalid: Why?

43. Exercise 2 If he loves me then he gives me some flowers. He gives me flowers. So, he loves me. Valid or Invalid: Why?

44. Exercise 3 Beckham is famous. Beckham is a football player. Therefore, Beckham is a famous football player. Valid or Invalid: Why?

45. Exercise 4 If it rains, the street will be wet. If the streets are wet, accidents will happen. Therefore, accidents will happen if it rains. Valid or Invalid: Why?

47. Deductive Soundness It should be obvious by now that validity is about the logical connection between the premises and the conclusion. When we are told that an argument is valid, this is not enough to tell us anything about the actual truth or falsity of the premises or the conclusion. All we know is that there is a logical connection between them, that the premises entail the conclusion. So even if we are given a valid argument, we still need to be careful before accepting the conclusion, since a valid argument might contain a false conclusion. What we need to check further is of course whether the premises are true. So never say things like “this statement is sound”/ “invalid” or “that argument is true”!

48. Deductive Soundness If an argument is valid, and all the premises are true, then it is called a sound argument. Of course, it follows from such a definition that a sound argument must also have a true conclusion. In a valid argument, if the premises are true, then the conclusion cannot be false, since by definition it is impossible for a valid argument to have true premises and a false conclusion in the same situation. So given that a sound argument is valid and has true premises, its conclusion must also be true. So if you have determined that an argument is indeed sound, you can certainly accept the conclusion. An argument that is not sound is an unsound argument. If an argument is unsound, it might be that it is invalid, or maybe it has at least one false premise, or both. So never say things like “this statement is sound”/ “invalid” or “that argument is true”!

49. Deductive Soundness Sound: Valid + All Premises are TRUE Unsound: Invalid + one of the premise is FALSE

50. Comprehension: 1. All invalid arguments are unsound. 2. All true statements are valid. 3. To show that an argument is unsound, we must at least show that some of its premises are actually false. 4. An invalid argument must have a false conclusion. 5. If all the premises of a valid argument are false, then the conclusion must also be false. 6. If all the premises and the conclusion of an argument are true, then the argument is valid. 7. All sound arguments are true. 8. Any valid argument with a true conclusion is sound.

51. Group Activity 20 minGroup discussion 5 minSummarize discussion findings 15 minGroup presentation & discussion The Group leader must submit their findings in hard or soft-copy format to the lecturer and send to his email before or during the next class.

52. Summary Deduction and Induction Deductive arguments Deductive arguments are arguments in which the conclusion is claimed or intended to follow necessarily from the premises. Inductive arguments Inductive arguments are arguments in which the conclusion is claimed or intended to follow probably from the premises. Deductively Valid and Sound 1. The premises and the conclusion of an invalid argument can all be true. 2. A valid argument should not be defined as an argument with true premises and a true conclusion. 3. The premises and the conclusion of a valid argument can all be false. 4. A valid argument with false premises can still have a true conclusion 5. A Sound argument is a valid argument with all the premises are true.

53. Any Questions?

54. The End – Thank You!

55. Failed!

56. http://mycriticalthinking.pbworks.com