Critical Thinking Mini-Lessons

Massimo Pigliucci is certainly correct in saying that “it is important for anyone interested in critical thinking and science to understand the difference between deduction and induction” (“Elementary, Dear Watson” May/June 2003). However, it has been several decades since logicians have defined that difference in terms of going from general to particulars or vice versa. His own example of deduction belies the problem. It doesn’t go from the general to the particular but from one general and one particular statement to another particular statement. All men are mortal. Socrates is a man. Therefore, Socrates is mortal. General statements aren’t needed at all in the premises of some deductive arguments. For example, “Socrates is a stonemason. Socrates is a philosopher. Therefore, at least one stonemason is a philosopher.” This is a valid deductive argument. “Rumsfeld is arrogant. Rumsfeld is Republican. Therefore, all Republicans are arrogant” is also a deductive argument, though an invalid one, going from particulars to the general.

Induction, says Pigliucci, “seeks to go from particular facts to general statements.” That is true sometimes, but not all the time. Jones was late yesterday so he’ll probably be late today is an inductive argument. I admit it is not a cogent argument, but cogency is a different matter.

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