1. Check for validity (if it is a deductive structure).2. Check for soundness (e.g. are the premises true?).3. Check for strong or weak sample sizes (if it is an

inductive argument).4. Check for unstated assumptions in the argument.5. Check for unwanted or absurd consequences of an

argument (i.e. assume the argument is sound).6. Check for informal fallacies.

HOW TO CRITIQUE AN ARGUMENT

• Difference between deductive and inductive reasoning

• Wason selection task (deductive arguments)• Tooby and Cosmides• Empirical and “a priori” evidence

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Deductive and Inductive arguments.

• There are two main kinds of arguments: Deductive and Inductive.

Deductive arguments make inferences from statements about GENERAL types or laws, to statements about SPECIFIC instances of the type/ law.

Inductive arguments make inferences from more SPECIFIC instances to more GENERAL types or laws.

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DEDUCTIVE

• Deductive arguments have premises using general statements and conclusions about specific facts.– I.e. If it is true that all swans are white, then I

know that this particular swan is white.

– P: All swans are white.– P: This is a swan.– C: This swan is white.

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• Deduction involves inferring from a general law, to specifics.

• I.e. “If it is snowing, it is cold.”• We can infer that on ANY day that it is

snowing, it will be cold TODAY. • Or, “All cats are mammals,” • We can infer that my cat and your cat are both

mammals.

• Deductive arguments aim to PROVE that the conclusion is true.

• Inductive arguments aim to show that the conclusion is PROBABLY (or most of the time) true.

• Arguments that use statistical probabilities are usually inductive.

• They aim at reliability: The reasons given reliably indicate the truth of the conclusion.

• Inductive arguments include arguments from analogy, argument to the best explanation, reductio ad absurdum, etc.

• (any argument that does not aim at guaranteed proof of the conclusion)

Inductive

• Inductive arguments have specific premises and a general conclusion.– I.e. People have observed (empirical evidence) 4

billion swans and they are all white. They conclude that ALL swans are white.

– P: This swan is white.– P: This swan is white. . . .– C: ALL swans are white.

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– Arguments that deal with probabilities and statistical evidence are Inductive.

– I.e. Empirical evidence shows that a billion known swans are white. Therefore, it is most likely true that “All swans are white.”

Inductive arguments

Inductive arguments

• 75% of college students graduate. • I’m a college student. • Therefore, I will probably graduate.

• “Most,” “Sometimes” “Probably” “Some”

• “60% of the thousand people we surveyed in Utah said they voted for Obama. So, maybe 60% of the people in the United States voted for Obama.”

• We inferred from a sample of Utahans to a population in the U.S.

Inductive arguments

• Inductive arguments cannot be “valid” or “invalid.”

• They can only be strong or weak, depending on sample size, reliability, etc.

• Sample size of 1 fails to offer reliable evidence.

Critiquing arguments1. Check for validity (if it is a deductive structure).2. Check for soundness (e.g. are the premises true?).3. Check for strong or weak sample sizes (if it is an

inductive argument).4. Check for unstated assumptions in the argument.5. Check for unwanted or absurd consequences of an

argument (i.e. assume the argument is sound).6. Check for informal fallacies.

• Reasoning and Human Nature

Wason Selection Task

• http://www.philosophyexperiments.com/wason/Default.aspx

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• You are a bouncer in a bar. • The rule is that you can only drink beer if you

are 21 or older. • Which people must you check?. . .

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• 80% get case 1 wrong. • 80% get case 2 right.

• Each case requires logical reasoning.• Case 1 is abstract.• Case 2 involves a social situation.

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• The reasoning in both cases is the same.

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Answers Case 1= card 1 and 4

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Case 2: Card 1 and 4

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• The reasoning involved in case 1 and 2 are the same.

• So, why is the beer-drinking case easier to solve?

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• Leda Cosmides and John Tooby :The Adapted Mind (1992)

They use the Wason Selection Task to show that we have an innate ability to reason about social situations, particularly when it involves “cheaters.”

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• Cosmides argues that this kind of cheater-detection is something that people -- like other primates -- are very good at, and that we are good at it because it is important to us, not only individually but also collectively and historically.

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• “It's important because the evolution of a stable propensity for altruism requires high-accuracy detection and punishment of cheaters. In a society in which individuals are free to choose different strategies about cooperation based on past experience, individuals who always cooperate will [succeed], while individuals who never cooperate will tend to be shunned.”. Tooby and Cosmides

• This requires that we be able to tell who is cheating and who is not.

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• The evolutionary-psychology reinterpretation is, "People are naturally good at detecting cheaters -- because this is an essential adaptation for the reciprocal altruism that is at the foundation of hominid social organization. People are not nearly as good at general hypothesis testing, because there has never been any similar selective urgency “

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Possible outline for Tooby and Cosmides

• P. Detecting cheaters is an essential adaptation for altruism.

• P. Altruism is necessary for a social organization.• P. If a “cheater-detection” mechanism wasn’t

innate, we wouldn’t have survived as a species. • P. Case 2 of Wason selection task is involves

detecting cheaters. • C. Being able to solve case 2 involves innate

cheater detection reasoning skills.

• Quiz for Friday:• Write one paragraph summary of one of the

articles under • REASONING TUTORIALS• Found under Course

ContentHandoutsReasoning Tutorials. • Turn it in class Friday.• I.e. articles on “assumptions,” “evaluating

claims,” “identifying arguments in prose,” etc.

Empirical and a priori

• Premises are shown to be true in two ways: Empirical (also, a posteriori) and a priori.

• Empirical evidence is drawn from observation. Empirical premises are factual statements about the world.

• I.e. “The cat is on the mat.” • I justify the statement by saying that I SAW or

observed the cat on the mat.

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• A priori evidence is not supported by observation.

• i.e. the statement, “2+2=4” is justified by reason, not by empirical observation.

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Empirical arguments

• Empirical arguments have at least one premise whose truth is supported by observation.

• I.e. • P1: Bees pollinate flowers.• P2. This is a bee.• C: This bee pollinates flowers. • The truth of Premise 1 is justified by empirical observation.

A priori arguments

• Derived by or designating the process of reasoning without reference to particular facts or experience.

• A priori arguments have NO premises whose truth is supported by empirical evidence.

• I.e. All bachelors are unmarried males.

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A priori knowledge.

• 40 plus 5 is equal to 45. • This information is known without direct

experience; You can calculate the problem as an abstract without needing to arrange forty-five objects and count them.

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Empirical or a priori?

• What about the statements:• “Electrons exist”• “Squares have four sides of equal length.”• “All bachelors are married.”• “The sun will rise tomorrow.”