Chapter 10

Chapter 10 - Chapter 10 Reasoning and...

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Chapter 10 Reasoning and decision-making - syllogistic reasoning: from a major and minor perspective, the reasoner must evaluate the conclusion. VS. Conditional reasoning. syllogistic reasoning: involves evaluating whether a conclusion necessarily follows deductively from two premises that are assumed to be true. The two premises are referred to as the major and minor premise. Their truth is taken as certain, regardless of whether the statements make any sense in the real world. -we are to ignore the semantics or the meaning of the premises altogether. The premises are simply assumed to be true for the sake of the argument. Because the syntax or structure is identical, their conclusions must be evaluated identically. -The only matter at hand is whether the conclusion must logically follow from the premises: valid deductive conclusion: a conclusion that is necessarily true given that the premises are true. a) Syllogistic forms -4 types of deductive reasoning are shown: the universal affirmative ((all A are B)), the universal negative ((no A are B)), ((some A are B)), ((some A are not B)). -3 steps to evaluating the conclusion according to the predicate calculus. 1) one must accurately consider all possible interpretations of the premises and the conclusion. 2) one must consider all possible combinations of meanings of the major and minor premises 3) one must determine whether all possible meanings of the conclusion are consistent with all possible combinations of the premises. b) Common errors: -when the major premise contains a universal affirmative statement and the minor premise is a particular affirmative statement, people regard a conclusion containing the word “some” as valid. They do the same thing if the major premise is also a particular affirmative statement. -by contrast, when the major and minor premises both are universal negative statements, people accept a conclusion that contains the word “no”. c) Cognitive constraints - atmosphere hypothesis: presumed that people don’t even attempt to evaluate the conclusion logically; was restated that if one or more of the premises accepted as negative, then the conclusion is generally accepted as negative; if one or more premises is a particular statement, then a particular conclusion is accepted; only accounts for part of the errors and misses the mark on others; provides no account of why intelligent college students would blindly follow these heuristics instead of trying to reason correctly i) the limitations of the working memory: students may forget or fail to represent in the first place some possible combinations of premises. Johnson and Steedman reported that reasoners try to simplify the combos of premises by avoiding those that call for class
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inclusion or subset relations. By contrast, simple combos of meanings are picked up readily. People consider only some of the premise combos when evaluating the conclusion. If a conclusion firs some but not all of the combos, then it may well be
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Chapter 10 - Chapter 10 Reasoning and...

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