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Unformatted text preview: Evaluating Arguments and Truth Claims (Critical Thinking, Chapter 8) LECTURE 12 Evaluating Arguments Once you have an argument summarized/standardized, you need to evaluate it to see if you are forced to accept the conclusion. There are two main questions to ask when doing so: Is the argument a "good argument"? Are the premises acceptable? When is an argument a good argument? What "good argument" does not mean: "agrees with my views" The attitude that only arguments that agree with your viewpoints are good is extremely close-minded. People aren't always smart and can be persuaded by "eloquent speech" (and be confused by solid reasoning). Hitler was more persuasive than Churchill, but that doesn't mean that Hitler's arguments were better. Although it's easier to tell whether an argument is good if it is well written, being well written doesn't make it good. Clarity, eloquence and organization can all occur in the presence of logical mistakes. "persuasive argument" "well-written/spoken" When is an argument a good argument? What "good argument" does mean. It must, at the least, be either deductively sound (valid with true premises) or inductively cogent (strong with true premises). In a nut shell, a good argument embodies all the good qualities of critical thinking. (See guidelines on p. 206.) When is an argument a good argument? But it will also need to be clear... An argument isn't good unless it is understandable. One needs to avoid equivocation and use exact language. Arguments with a lot of irrelevant material can't be said to be good arguments. Arguments that contain logical contradictions commit the fallacy of inconsistency. If an arguer ignores facts relevant to the conclusion at hand, we can't say the argument is good (it doesn't account for relevant objections). An argument can't be good if it hastily dismissed objections. ...precise... ...the premises need to be relevant... ...consistent... ...complete... ...and fair. When is it reasonable to accept a premise? Arguments always contain premises, and--while some premises will have support from other premises --there will always be some premises that are mere assumptions (claims made by the arguer). If the argument is valid/ strong, its soundness/cogency will turn on whether these assumptions are true. So how can we tell if we should accept them? The Principle of Rational Acceptance: It is reasonable to accept a claim if... (1) The claim does not conflict with personal experience that we have no good reason to doubt it. (2) The claim does not conflict with background beliefs that we have no good reason to doubt. (3) The claim comes from a credible source. Does the claim conflict with your experience? In general, you should favor the testimony of your own sight (and other senses) over the testimony of others. If someone tells you her Doberman is gentle as a kitten, but you've seen him attack many people, you should probably not believe that the Doberman is gentle. But it should be noted that your senses are not indubitable (un-doubtable). They can be mistaken for any number of reasons. Bad physical conditions (e.g., poor lighting) Sensory impairment (e.g., poor vision) Observer impairment (e.g., drunk) Unreliable measuring instruments How reliable are your senses? How reliable are your senses? How reliable are your senses? Just how are are you supposed to to count how many times "are" appears in this quote? Does the claim conflict with background beliefs Background beliefs: convictions held--usually assumed without question--that inform most of the other beliefs that we have. e.g., It snowed in Las Vegas last July 4th. This seems to contradict our background belief that it doesn't snow in deserts during the summer. e.g., George W. Bush is a robot. This contradicts our background belief that people aren't robots. But it is important to note that even background beliefs should be subject to revision if sufficient evidence is presented against them (don't be dogmatic about any beliefs you have). Group Work Exercise 8.1 Pages 208-209 Does the claim come from a credible source? Much of what we believe is based on the testimony of sources. We saw a lot about this in chapter 6 (more is in chapter 12). Does the claim come from a credible source? To reiterate: questions to ask to determine source credibility: Genuine expert? Are they outside their area? Are they biased? Do they have a reason to lie? Questionable senses (were they drunk)? Are they generally reliable (is it The Enquirer? ) Right context? Can expert opinion settle the issue (e.g., is this a moral issue)? Is it improbable? Group Work Exercise 8.2 Pages 210-211 Refuting Arguments There are two ways to refute an argument: Show that a premise--or a critical group of premises--is false or dubious. Show that the conclusion does not follow from the premises. Showing Premises False If a premise is critical to an argument, showing it false will refute the argument. (1) All presidents live in the White House. (2) Paris Hilton is President. So, (3) Paris Hilton lives in the White House. Showing (2) to be false is sufficient to refute the argument. Showing Premises False However, showing false an irrelevant premise will not refute the argument. (1) All circles are squares. (2) All squares are rectangles. (3) All rectangles are geometrical figures. (4) So, all squares are geometrical figures. Showing (1) is false won't keep (2) and (3) from proving (4). Showing Premises False Additionally, for refutation, the premise must be necessary (critical) (1) TJ is a bachelor. (2) TJ is an uncle. (3) So, TJ is a Male. Since both (1) and (2) provide independent support for (3) falsifying only one of them will not refute the argument. Showing Premises to be Dubious and other Techniques If one shows a critical premise to be doubtable, then one has refuted the argument (by showing it to be unconvincing). Demonstrating doubt: Appeal to personal experience, common knowledge, or reputable source. Note a self-contradiction (either in a single premise or between premises). Show the premises is based on an unwarranted assumption. Personally demonstrate its falsity or dubiousness. Showing Premises to be Dubious and other Techniques Other refutation Techniques: Reducing to the absurd (reductio ad adsurdum): Show the truth of a premise would entail something clearly false (absurd). Roomate: Absolutely all killing is wrong. You: Point out that this implies that it is wrong to eat any plants or animals (since this would involve killing). Showing Premises to be Dubious and other Techniques Other refutation Techniques: Present a counter-example: present an exception that shows a premise false. Roommate: All 20th Century presidents were rich. You: Harry Truman wasn't! Showing That the Conclusion does Not Follow from the Premises. To do this, you need to show that the argument is either (a) deductively invalid or (b) inductively weak. Most important questions: If deductive, does the conclusion follow necessarily from the premises? Are the premises relevant (is there a fallacy)? Are the premises sufficient to support the conclusion? Does the argument omit any crucial countervailing evidence? Showing That the Conclusion does Not Follow from the Premises. Example 1: Get high-speed internet access by satellite. It's fast, reliable, and won't tie up your phone lines. But what about costs (installation fee & high monthly payments)? What about long term contracts? Showing That the Conclusion does Not Follow from the Premises. Example 2: All mothers should stay home with their young kids. It would promote closer family ties, and studies show that children with stay-at-home moms do better in school, have higher self-esteem, and are less likely to get involved with drugs or commit crimes. But many mothers have to work to make ends meet The social and economic costs of removing working mothers from the workforce would be enormous. Group Work Exercise 8.3 Pages 216-217 ...
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This note was uploaded on 09/08/2010 for the course LING 21 at San Jose State University .