Deductive Reasoning

Deductive Reasoning - Deductive Reasoning Decision Making Chapter 12 Complex Cognitive Tasks Deductive reasoning and decision making are complex

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1 Deductive Reasoning & Decision Making Chapter 12 Complex Cognitive Tasks Deductive reasoning and decision making are complex cognitive tasks that are part of the thinking process. Thinking Problem Solving Decision Making Deductive Reasoning Deductive Reasoning

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2 if there are clouds in the sky then it will rain. Is a process of thinking in a logical way, where conclusion are drawn from the information given, for example: Deductive Reasoning Information Conclusion There are two kinds of deductive reasoning: Deductive Reasoning 1. Conditional Reasoning 2. Syllogisms Conditional Reasoning Conditional reasoning (or propositional reasoning), tells us about the relationship between conditions. Conditional reasoning consists of true if- then statements, used to deduce a true conclusion. Though the premises may be true the conclusions can be valid or invalid .
3 Valid Conclusion Jenna is in cognitive psychology class So Jenna must have completed her general psychology requirements. If a student is in cognitive psychology, Then she must have completed her general psychology requirements. Premises Observation Conclusion Valid Conclusion David has NOT completed his general psychology requirements. So David must NOT be in cognitive psychology class. If a student is in cognitive psychology, Then she must have completed her general psychology requirements. Valid Conclusions Affirming the antecedent If p is true then q is true p is true q is true Modus ponens Valid If Newton was a scientist, then he was a person Newton was a scientist Newton was a person Denying the consequent If p is true then q is true q is not true p must be not true Modus tollens Valid If an officer is a general, then he was a captain. Gerald is NOT a captain, So he NOT a general.

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4 Invalid Conclusions Affirming the consequent If p is true then q is true q is true p is true Invalid If this is a carrot, then it is a vegetable This is a vegetable So this is a carrot Denying the antecedent If p is true then q is true p is not true q must be not true Invalid If Reagan is a rocket scientist, then he is human Reagan is NOT a rocket scientist, So he is NOT a human Invalid Conclusions Portion of the Statement Antecedent Consequent Affirm It is an apple Then it is fruit Affirming the Antecedent (valid) It is a fruit Then it is apple Affirming the consequent (invalid) Deny It is NOT an apple Then it is NOT a fruit Denying the antecedent (invalid) It is NOT a fruit Then it is NOT apple Denying the consequent (valid) If this is an apple, Then it is fruit Daily Life Some valid examples of propositional logic in our daily life. 1. Parking permitted between 6:00-7:00 PM. If the time is between 6:00-7:00 PM then parking is permitted. It is 6:30 …therefore parking is permitted ( affirming the antecedent, valid ) 2. If Tom is found guilty, he is going to jail. Tom did not go to jail therefore he was not guilty ( denying the consequent, valid )
5 Syllogisms Another form of deductive reasoning is called

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This note was uploaded on 03/09/2010 for the course PSY 3153 taught by Professor Ahmad during the Fall '09 term at Henderson.

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Deductive Reasoning - Deductive Reasoning Decision Making Chapter 12 Complex Cognitive Tasks Deductive reasoning and decision making are complex

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