# chpater 8 - Logic and reasoning [14] Oct 17 2011 Chapter 8...

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Logic and reasoning [14] Oct 17 2011 Chapter 8 Inductive reasoning -- Do the homework! – -- Reach out if in trouble -- Two kinds of arguments - Deductive - Inductive - Deductive: conclusion follows 100% - Inductive: less than 100% Examples: - deductive: If it’s raining, John sleeps. It’s raining. Therefore, John sleeps. - inductive: Each time I took it, aspirin cured my headache. Today I have a headache, and I took an aspirin. My headache will go away. Inductive arguments: - strong: support for the conclusion is very good (high %) - cogent: strong + premises are true The study shows that 90% of all left-handed people die in an airplane crash. Therefore Phil, who is left- handed, is very likely to die in an airplane crash. Inductive arguments: - strong: support for the conclusion is very good (high %) - cogent: strong + premises are true The study shows that 70% of people whose tumors are detected at a very early stage survive cancer. Therefore Phil, whose tumor was detected very early, will survive. Why inductive logic? - Deductive logic: mathematics, computer-science, etc. (axiomatizable, abstract sciences) - Inductive logic: concrete, ‘empirical’ science (physics, chemistry, biology, geology, economics, etc.)

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Why inductive logic? - Deductive logic: mathematics, computer-science, etc. (axiomatizable, abstract sciences) - Inductive logic: concrete, ‘empirical’ science (physics, chemistry, biology, geology, economics, etc.) Does not take us beyond what is given in the premises! It only makes explicit what is in them. - All humans are mortal. - Socrates is human. -- Socrates is mortal. Why inductive logic? - Deductive logic: mathematics, computer-science, etc. (axiomatizable, abstract sciences) - Inductive logic: concrete, ‘empirical’ science (physics, chemistry, biology, geology, economics, etc.) Does not take us beyond what is given in the premises! It only makes explicit what is in them. - All humans are mortal. - Socrates is human. -- Socrates is mortal. Does take us beyond what is given in the premises! It goes ‘beyond’ evidence. - We picked up 999 balls from the urn and all were red. -- The next ball we pick will be red. Three types of inductive arguments - Enumerative induction (parts b whole) - Analogical induction (X :: Y b A :: B) - Causal induction / reasoning (shared causal properties) Enumerative Induction: An inductive argument pattern in which we reason from premises about individual members of a group to conclusions about the group as a whole . 80% of the apples in the crates we examined are good. Therefore, approx. 80% of all apples we picked today are good. Enumerative Induction: An inductive argument pattern in which we reason from premises about individual members of a group to conclusions about the group as a whole . 20% of the students I examined today
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## This note was uploaded on 12/20/2011 for the course PHIL 102 taught by Professor Rug during the Fall '11 term at University of Illinois, Urbana Champaign.

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chpater 8 - Logic and reasoning [14] Oct 17 2011 Chapter 8...

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