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Unformatted text preview: 1 CC2002 Semester One 2011/12 Creative and Critical Thinking Lecture 6 Deductive Reasoning (II) 2 The ambiguity of 1. Possible ( ) (logical possibility) 2. Probable ( ) (empirical probability) ( ) ( ) (= ) 3 What strong arguments are A strong ( ) argument: 1. Invalid ( ) 2. Given that the premise(s) is(are) true, it is very likely ( ) that the conclusion is true . E.g. 1. 99.9% CCT 2. CCT 3. 1. Peter bought one ticket in a fair lottery with ten million tickets. 2. So Peter is not going to win the lottery. 4 What strong arguments are (>50% <100%) 5 Deductive Argument ( ) A deductive argument is an argument in which the conclusion is claimed to be justified by (or to follow from) the premise(s) with (logical) necessity ( ), or it is claimed to be (logical) necessary that the conclusion is true if all the premises are true. 180 All whales are mammals. All mammals are animals. Hence, all whales must be animals. Alan is a father. Therefore, it is necessary that Alan is a male. Please note that: Deductive arguments valid arguments 6 Inductive Argument ( ) An inductive argument is an argument in which the conclusion is claimed to be justified by (or to follow from) the premise(s) with a certain degree of probability ( ), namely > 0.5 , or The conclusion is claimed to be probably true ( ), (i.e., more likely to be true than false) if all the premises are true. 95% of our students wear glasses. Joe is our student. Therefore, Joe probably( ) wears glasses. Mary is a sixyearold girl. Therefore, it is very likely that Mary cannot finish 100m in 15 seconds....
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 Spring '97
 KEITHCHAN

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