Argument Basics. When an argument shows that its conclusion is worth accepting we say that the argument is good.

Transcription

1 Argument Basics When an argument shows that its conclusion is worth accepting we say that the argument is good. When an argument fails to do so we say that the argument is bad. But there are different ways for an argument to be good or bad because there are different types of arguments.

2 Two types of arguments 1) Deductive Argument 2) Inductive Argument

3 (1) Deduction: Reasoning from general principles to particular cases 1. The sum of the interior angles of any triangle is 180 degrees. 2. ABC is a triangle. 3. Angle A = 50 degrees. 4. Angle B = 40 degrees. Therefore C. Angle C = 90 degrees. In deductive arguments, the premises entail the conclusions. This is a very powerful form of reasoning. If the premises are true and the form is valid, then conclusion must be true.

4 (2) Induction: Reasoning from particular cases to general principles 1. Helium is a gas and it has a low density at 1ATM & 22C. 2. Oxygen is a gas and it has a low density at 1ATM & 22C. 3. Nitrogen is a gas and it has a low density at 1ATM & 22C. Therefore C. All gases have a low density at 1ATM and 22C. In inductive reasoning the premises support the conclusion in direct proportion to the extent and comprehensiveness of the available data.

5 A philosophical aside In praise of induction and risk Valid [deductive] arguments are risk free. Inductive logic studies risky arguments. A risky argument can be a very good one, and yet its conclusions can be false, even when the premises are true. Most of our arguments are risky. Ian Hacking, Introduction to Probability and Inductive Logic, 11. A inference rule is amended it yields an inference we are unwilling to accept; and inference rule is amended if it violates a rule we are unwilling to amend. All this applies equally well to [deduction and] induction. Predictions are justified if they conform to valid canons of induction; and the canons are valid if they accurately codify accepted inductive practice. Nelson Goodman, Fact, Fiction and Forecast, 64. Important Note: (i) No inductive argument meets the standard of deductive validity. (ii) No deductive argument meets the standard of inductive validity.

6 (3) Analogical reasoning: Similar cases ought to be treated similarly 1. A is relevantly similar to B. 2. A has property P. Therefore C. B has property P. Meeting the G condition here is different from either deduction or induction. (Assuming that Premise 2 is acceptable) it all comes down to the claim of relevant similarity.

7 (4) Conductive Reasoning: Weighing pros and cons, arguments and counterarguments Conductive arguments can typically involve a blend of the above three. You strengthen a conductive argument by explicitly conceding and attempting to address counter-considerations. E.g., the question of affirmative action Again, here, meeting the G condition is not simply deductive validity, sufficient inductive support, or a strongly compelling analogy; this a a fourth (and most complex) way of meeting the G condition.

8 Interpreting Arguments (i) Standardizing Arguments What is the C? What are the P s? (ii) Patterns of Premises How exactly are the P s organized and interrelated? (iii) Unstated Premises and Conclusions Filling in what is left unsaid (and left for you to fill in). (iv) Charity in Interpretation Be kind! Avoid the temptation to portray an argument poorly.

9 Argument Structure In order to evaluate an argument, it is obviously crucial to first understand exactly what the argument is. Step 1: identify premises and conclusions Step 2(a): identify the content of the premises and conclusion Step 2(b): identify the form or structure of the argument

10 Standardizing Arguments (I) To standardize an argument is to explicitly set apart its conclusion and its premises. Standardizing arguments should not be confused with formalizing or schematizing arguments. Procedure: (i) (ii) Find the conclusion. What is the passage trying to make me believe? Find the premises. What claims are being offered to support the conclusion.

11 Standardizing Arguments (II) Be careful! Be thoughtful! In written and spoken exchanges, conclusions are often scattered among premises and irrelevant material in the passage you are evaluating. Conclusions may be asserted first, last or in the middle of a passage. This makes arguments difficult to evaluate. In good editorials, conclusions are asserted first. In good analytical writing, conclusions are asserted last. In general, it is a sign of bad writing that conclusions are asserted in the middle.

12 Example (I) Research by Professor Fizzbane has shown conclusively that all humdingers are zipwags. Interestingly, our research at Gentech labs has shown that the rare spittleburg collected from Amazonia is also a humdinger. We conclude, uncontroversially, that the spittleburg is a zipwag. Hermione Granger, Recent Gentech Research

13 Example (I) Analysis Here is the standardized argument. Premise 1: All humdingers are zigwags. Premise 2: This spittleburg is a humdinger. Conclusion: This spittleburg is zigwag. We would formalize the argument as follows: Premise 1: All P are Q Premise 2: R is P Conclusion: Therefore, R is Q

14 Example (II) At Stalingrad, General Chuikov faced an unhappy dilemma. On the one hand, he could order a further retreat in the face of the German advance. This would result in significant losses to the 62 nd army. On the other hand, he could order the army to stand its ground at Stalingrad. That, too, would result in heavy losses.

15 Example (II) Analysis Here is the standardized argument: 1: Either we retreat further or we stand our ground. 2: If we retreat, then we will suffer heavy losses. 3: If we stand our ground, then we will suffer heavy losses. 4: Therefore, we will suffer heavy losses. Here is the formalized argument: Premise 1: Either P or Q. Premise 2: If P then R. Premise 3: If Q then R. Conclusion: R.

16 Scope The scope of a claim can be understood as the coverage of the claim. (i) Universal claims. Cover all. All toddlers love toy cars. Every toddler loves toy cars There is no toddler that does not love toy cars. (ii) Particular claims Cover some. Some toddlers love toy cars. A few toddlers love toy cars. There is a toddler that loves toy cars.

17 Degrees of Commitment People s commitment to their conclusions vary. They may be more or less committed to a conclusion. It is certain that It is indubitable that It is probable that It is likely that It might be true that It could be true that

18 Organization of Premises Premises may be organized in different ways. There are (i) convergent premises, and (ii) linked premises Sometimes called convergent support, and linked support.

19 Convergent Premises Convergent premises (also convergent support) are completely independent, and each individually adds to the case in favor of the conclusion. The failure of an individual premise does not necessarily indicate the failure of the whole argument. Convergent premises: P1 P2 P3 C1

20 Example of Convergent Premises David Dangoor, Phillip Morris in a Rolling Stone interview I ll tell you what I like about this business. First, there are no surprises. There is nothing more to be said or discovered about cigarettes. Second, no new company wants to get into the tobacco business. That s great. Third, we have the best partners in the world: the governments. In a lot of countries, the taxes from our product are incredibly important to the whole welfare state. So, no matter how you look at it, this is a great business to be in if you can handle the fact that some people are not going to like you.

21 Example Standardized P1: There is no more negative evidence forthcoming about tobacco. P2: No one today wants to get into the tobacco business. P3: Tobacco companies have the best partners in the world. Therefore C1: The tobacco business is a great business to be in if you can handle the fact that some people are not going to like you.

22 Linked Premises Linked premises (also linked support) are interdependent in their support for the conclusion. Linked Premises P1 + P2 + P3 C1 Linked arguments are only as strong as their weakest link. If any link fails, then the argument fails.

23 Example of Linked Support Anyone who uses weapons that predictably injure civilians is acting immorally. Cluster bombs predictably injure civilians. Those jerks are still today using cluster bombs. Therefore, they are acting immorally. [p.41]

24 Example Standardized P1: Anyone who uses weapons that predictably injure civilians is acting immorally. P2: Cluster bombs predictably injure civilians. P3: A group of people is using cluster bombs. C1: That group is acting immorally.

25 Subarguments Arguments often proceed in stages. A statement that serves as the conclusion of one argument becomes a premise in another argument. Subarguments may be provided to support controversial premises.

26 Example of Subargument (I) A computer cannot cheat in a game, because cheating requires deliberately breaking the rules in order to win. A computer cannot deliberately break rules because it has no freedom of action.

27 Example of Subargument (I) P1: A computer has no freedom of action C1 (P2): A computer cannot deliberately break rules. P3: Cheating requires deliberately breaking rules. C2: A computer cannot cheat.

28 Example of Subargument (I) 1. A computer has no freedom of action. Thus 2. A computer cannot deliberately break rules. 3. Cheating requires deliberately breaking rules. Therefore C. A computer cannot cheat C

29 Unstated Conclusions Sometimes conclusions are left implicit. This is often an effective rhetorical device as it forces the listener to contribute to, and thereby participate in, the argument. Consider the following cases: The law does not permit suicide, and whatever the law does not explicitly permit it forbids. Aristotle Could evolution ever account for the depth of intellect that Carl Sagan possesses? Not in a billion years. (p.51)

30 Supplementing Unstated Material P1. The law does not permit suicide. P2. Whatever the law does not explicitly permit it forbids. Therefore C. Suicide is illegal. P1. Evolution cannot account for the depth of intellect that Carl Sagan possesses. Therefore C. The theory of evolution is false.

31 Unstated Premises The question of unstated premises gets us into more subtle terrain, because all communication relies on a vast implicit background of shared beliefs and values. In general, in any conversation, we do not explicitly articulate everything that is relevant. Sometimes, one of these implicit background beliefs must be explicitly added when standardizing an argument, on the grounds that: (i) The author clearly seems to be committed to it (ii) Explicitly adding it greatly improves the force or clarity of the argument

32 Example (I) [P0: Freedom of action is required to deliberately break rules.] P1: A computer has no freedom of action C1 (P2): A computer cannot deliberately break rules. P3: Cheating requires deliberately breaking rules. C2: A computer cannot cheat.

33 Former US President Jimmy Carter, Just War or a Just War? from The New York Times (9 March 2003). Profound changes have been taking place in American foreign policy, reversing consistent bipartisan commitments that for more than two centuries have earned our nation greatness. These commitments have been predicated on basic religious principles, respect for international law, and alliances that resulted in wise decisions and mutual restraint. Our apparent determination to launch a war against Iraq, without international support, is a violation of these premises.

34 Standardized 1. America s reputation was staked on commitment to certain key principles. 2. These principles are based on religious principles, respect for international law, and important alliances. 3. Adherence to these principles has usually resulted in wise decisions. 4. Attacking Iraq without international support would violated these principles. Therefore C. America should not attack Iraq without international support

35 Be Careful! No supplementation without justification Guidelines for when to add missing premises 1) Logical gaps indicative of missing premise(s). 2) Additional premise is implicitly or explicitly accepted by the arguer. 3) Statements of missing premises should be as plausible as possible.

36 The Principle of Charity: Be Charitable! Bend over backwards to be fair to the arguer. Reid on Hume: Temper, moderation, and good manners. In other words: Begin with the assumption that the argument is cogent. Do not add material to an argument that makes it a worse argument. Assume that the arguer will be responsive to reasoned counter-arguments.

37 Wisdom from your textbook! On the presumption that people who offer arguments are seeking to be reasonable, and to provide information supported by logically connected ideas, we should not represent their argument as implausible or unreasonable unless there is compelling evidence for doing so. [p.60]

38 Final Example III Mill, On Liberty (1859) The peculiar evil of silencing the expression of an opinion is that it is robbing the human race; posterity as well as the existing generation; those who dissent from the opinion still more than those who hold it. If the opinion is right, they are deprived of the opportunity of exchanging error for truth. If it is wrong, they lose what is almost as great a benefit, the clearer perception and livelier impression of truth, produced by its collision with error.

39 1. If an opinion that is right is censored, then those who mistakenly think that it is wrong are deprived of the opportunity of exchanging error for truth. 2. If an opinion that is wrong is censored, then those who correctly think that it is wrong are robbed of almost as great a benefit Thus 3. Those who dissent from a censured opinion are wronged to an even greater extent than those who agree with the censured opinion. 4. If an opinion that is right is censored, then those who correctly agree with the censored opinion are also wronged. Thus 5. Silencing the expression of an opinion robs the human race, both present and future generations. Therefore C. Censorship is wrong.

40 Example III Diagram C

41 A counter-argument Sometimes opinions are particularly volatile, and can have harmful consequences. This is why we have laws against hate literature. We are not free simpliciter, but rather, only free to the extent that our actions do not impinge the freedoms of others. Whenever opinions can predictably have the consequence of impinging on the rights and freedoms of others, they should be censured.

42 Standardized 1. Like all rights and freedoms, freedom of expression of opinion is essentially qualified and restricted. 2. One is only entitled to a certain right or freedom to the extent that it does not impinge on the rights and freedoms of others. 3. Some opinions impinge on the rights of others. Therefore C: Whenever opinions can predictably have the consequence of impinging on the rights and freedoms of others, they should be censured.

43 Three Key Logical Terms (1) Cogency (2) Soundness (3) Validity

44 (1) Cogency Cogency: A general property of arguments that reflects the extent to which an argument compels or constraints. A cogent argument satisfies the ARG conditions. An argument may be said to be cogent or lack cogency. Does admitting that an argument is cogent commit you to the conclusion? In some cases yes and in others no. It depends on the mode of reasoning at work! Strangely, as a matter of style and convention, we usually don t use the term cogent in cases where admitting the cogency of the argument would, in fact, absolutely commit us to the conclusion. Typically, the use of cogent to describe an argument often indicates a tentative commitment to the argument.

45 (2) Soundness Soundness: An argument is sound if the premises of the argument are true and the conclusion is implied by the premises. A sound argument satisfies the ARG conditions. Committing to the soundness of an argument is to commit to the truth and relevance of the premises as well as the acceptability of the form of the argument. Deductive arguments have the highest standard of cogency. Thus, we seldom describe deductive arguments, involving deductive entailment, as cogent. We usually described them as sound. A sound argument has true premises that deductively entail the conclusion. A sound argument is an argument that has the highest standard of cogency.

46 (3) Validity In day-to-day life, we talk about a valid driver s license, or the validation of software serial number. Validity is a technical term in deductive logic. If an argument has an appropriate deductive form, then we say that the argument is valid. Recall: deductive logic is just one mode of reasoning, though it is a very powerful form of reasoning. An argument is either valid or invalid. When we say that an argument is invalid we mean that we are rejecting the argument because it doesn t have the right deductive form. When we say this, we don t care about the content of the premises. That is, we don t care what the premises are about.

47 (3) Validity (more) If an argument has a valid form and the premises are true, then the conclusion of the argument must be true. The conclusion is deductively entailed. But, an argument may be valid (have the right form or structure) but not be true. It s premises could be false. Important: Committing to the validity of an argument, does not necessarily commit you to the truth conclusion. Likewise, asserting the invalidity of an argument, does not necessarily commit you to rejecting the conclusion. (You might accept the conclusion, but reject the form of the argument given for the conclusion.)

48 Validity Illustrated P1: If it s whirly-gig then smack-gurgle. P2: This is a whirly-gig. C1: This is also a smack-gurgle. This is a valid argument. We recognize the form as being valid. All arguments of this form are valid: P1: If P then Q. P2: P C1: Therefore, Q But, not all arguments of this form necessarily produce true conclusions. In this case, we don t know if the premises are true or false. We only know that argument is valid. We know nothing about its truth!

49 Example 1: Important! Validity and Truth are Different. P1: All men are mortal. P2: Socrates is a man. C1: Socrates is mortal. Valid and True. Example 2: P1: All men are purple. P2: Socrates is a man. C1: Socrates is purple. Valid but false. Note that Example 1 and Example 2 have exactly the same form or structure of argument.

50 A Practical Aside Sometimes you will hear valid applied to other modes of reasoning. For example, you might hear: That s a valid analogy. This is generally a mistake or error. As a matter of style and convention, we reserve the word valid for deductive arguments that have an appropriate form. Sometimes you will hear sound applied to other modes of reasoning. For example, you might hear: That s a sound analogy. This is generally an mistake or error. Likewise, we also usually reserve the term sound for deductive arguments that have true premises and entail the conclusion. Cogence is usually the positive term used to describe arguments that use modes of reasoning other than deduction. In technical discussion you might here someone refer to a sound induction or a valid induction. This is often simply a mistake but sometimes a controversial philosophical point is being made