1. Invitation to Critical Thinking Chapter 9 Lecture Notes Chapter 9

2. Invitation to Critical Thinking Chapter 9 Overview: Types of Inductive Reasoning Presumptions and the “Burden of Proof” Plausibility Reasoning Hypothetically Explanatory Power Testing Hypotheses Causal Reasoning

3. Invitation to Critical Thinking Chapter 9 Presumptions and the “Burden of Proof” “Burden of Proof” reasoning is a kind of inductive reasoning Useful in resolving disputes that cannot be compromised, or reconciled on a win/win basis The greater the risk of error - and the higher the cost associated with being wrong - the heavier the burden of proof Who has the burden of proof?

4. Invitation to Critical Thinking Chapter 9 Plausibility Plausibility is a measure of how well we think an idea is likely to survive critical scrutiny The less plausible the arguer's position, the heavier the burden of proof The affirmative side in a debate has the burden of proof because it is so much harder to prove the negative Neither plausibility nor implausibility are absolute Some claims are more plausible than others In general, the more plausible the explanatory hypothesis, the stronger the inference

5. Invitation to Critical Thinking Chapter 9 Reasoning Hypothetically Inductive reasoning that consists in reasoning from facts or observations to explanatory hypotheses –An “explanation” is an idea or set of ideas that succeeds in reducing or eliminating puzzlement –An “explanatory hypothesis” is an idea or set of ideas put forward for that purpose –“Hypothesis” means supposition or conjecture

6. Invitation to Critical Thinking Chapter 9 When reasoning hypothetically The conclusion does not follow deductively from the premise The premise makes it reasonable to suppose that the conclusion is true –though there remains room for doubt about the truth of the conclusion The inference to a classification is a reasonable induction –if the conclusion were true, that would explain the truth of the premise -- or – –if the conclusion were not true, that would make the premise much more puzzling

7. Invitation to Critical Thinking Chapter 9 Hypothetical reasoning lies in its capacity to extend or expand our knowledge of the world Since hypothetical reasoning always takes us beyond what we already know, it always involves the risk of error Just as with inductive generalizations –the strength of an inference to an explanatory hypothesis is essentially a matter of how well the risk of error is managed or controlled –There really is no way to manage the risk of error in hypothetical reasoning on an individual inference-by-inference basis

8. Invitation to Critical Thinking Chapter 9 Explanatory Power Explanatory power of a given hypothesis –the capacity it has to reduce or eliminate puzzlement The greater the explanatory power of a given hypothesis, the stronger the inference Relative explanatory power –Compare the explanatory hypothesis under investigation with other hypotheses When comparing equally powerful competing hypotheses or when several competing hypotheses are powerful –Appeal to the plausibility standard when the explanatory power standard is not decisive –Test hypotheses experimentally

9. Invitation to Critical Thinking Chapter 9 Testing Hypotheses Hypothesis An idea (or set of ideas) under investigation To investigate hypotheses –search for experimental evidence relevant to their truth or falsity –The scientific method Use the hypothesis under investigation to predict things See whether or not the predictions turn out to be true If what the hypothesis predicts turns out to be true that counts in favor of, or "confirms", the hypothesis If what the hypothesis predicts turns out not to be true that counts against, or "disconfirms", the hypothesis

10. Invitation to Critical Thinking Chapter 9 In testing hypotheses We should search for both confirming and disconfirming evidence –The stronger the evidence, the more certain the prediction –Disconfirming evidence weighs more heavily than confirming evidence –Confirming evidence does not completely verify the hypothesis –But notice that disconfirming evidence completely refutes it If we search thoroughly for disconfirming evidence and find none, that in itself constitutes a kind of confirming evidence –Referred to as "indirect confirmation" Every unsuccessful attempt to falsify a hypothesis has the effect of strengthening it

11. Invitation to Critical Thinking Chapter 9 Causal Reasoning David Hume We never directly observe causal relationships We have to infer them We can never infer them with deductive certainty –evidence for a causal relationship is always indirect, there will always be some room for doubt We can reason about causes by means of simple inductive generalization –turns out not to be very reliable –inductive generalization by itself provides no basis for distinguishing between a causal relationship and a mere coincidence

12. Invitation to Critical Thinking Chapter 9 Causal Reasoning John Stuart Mill Method of Agreement –The cause will be present in every instance in which the effect occurs –The more isolated the common antecedent condition, the more likely it is to be causally related to the effect

13. Invitation to Critical Thinking Chapter 9 Causal Reasoning John Stuart Mill Method of Difference—a variation of simple inductive generalization Look for a correlation between the absence of the effect and the absence of an antecedent condition The method of difference is not absolutely conclusive –any collection of individuals will have not one but very many different antecedent conditions in common –most conditions will have no causal connection with the effect The cause will be absent from every instance in which the effect does not occur The more isolated the difference, the more likely it is to be causally related to the effect

14. Invitation to Critical Thinking Chapter 9 Causal Reasoning John Stuart Mill Method of agreement and the method of difference each enhance the reliability of inductive inferences about causal relationships when used separately So it is reasonable to suppose that using them together would strengthen the inductive inference to a causal relationship even further

15. Invitation to Critical Thinking Chapter 9 Causal Reasoning John Stuart Mill Method of Concomitant Variation To apply the method of difference –Find or experiment to bring about an instance in which a suspected causal antecedent condition is out of the picture When it is difficult or impossible to eliminate a suspected cause –Vary it or observe its natural variations – See whether these variations are accompanied by corresponding variations in the effect under investigation

16. Invitation to Critical Thinking Chapter 9 Exercise 9.7 A few years ago the upstart Fox television network surprised a lot of people in the television industry by running a rather primitively drawn cartoon about a dysfunctional family at the same time as the nation's consistently top rated prime-time television program, The Cosby Show. The Simpsons knocked The Cosby Show out of first place and went on to several successful seasons, establishing the Fox network as a force to be reckoned with. What accounts for the success of The Simpsons? Consider the following list of explanatory hypotheses in terms of plausibility and explanatory power. On this basis narrow the list down to two leading hypotheses. Describe the kinds of experimental evidence that would then be needed in order to choose between the two finalists. –The Simpsons was more daring in its humor than the safe and mainstream Cosby Show. –It was racism. The Simpsons is about a white family and The Cosby Show was about a black family. –It was just a fluke. –It was novelty appeal. The Cosby Show was getting old. People were looking for something new. –The Simpsons was more challenging and rewarding intellectually than The Cosby Show.