Deductive / Inductive Arguments

December 17th, 2009

Deductive And Inductive Arguments

Copi and Cohen ((Irving M. Copi & Carl Cohen, Introduction to Logic (Twelfth Edition) (Prentice Hall, 2005), pp. 12-15.)) tell us that every argument makes the claim that its premises provide grounds for the truth of its conclusion; that claim is the mark of an argument.

But, there are two very different ways in which a conclusion may be supported by its premises, and thus there are two great classes of arguments: The deductive and the inductive. Understanding this distinction is essential in the study of logic.

Deductive Argument
Claims to support its conclusion conclusively.

Inductive Argument
Claims to support its conclusion only with some degree of probability.

A deductive argument makes the claim that its conclusion is supported by its premises conclusively. An inductive argument, in contrast, does not make such a claim. Therefore, if we judge that in some passage a claim for conclusiveness is being made, we treat the argument as deductive; if we judge that such a claim is not being made, we treat it as inductive. Since every argument either makes this claim of conclusiveness (explicitly or implicitly) or does not make it, every argument is either deductive or inductive.

Sextus Empiricus questioned the validity of inductive reasoning. “When they propose to establish the universal from the particulars by means of induction, they will effect this by a review of either all or some of the particulars. But if they review some, the induction will be insecure, since some of the particulars omitted in the induction may contravene the universal; while if they are to review all, they will be toiling at the impossible, since the particulars are infinite and indefinite.” ((Sextus Empiricus. Outlines of Pyrrhonism trans. R.G. Bury (Loeb edn) (London: W. Heinemann, 1933), p. 283.))

Logic – For the love of it

Jeffrey Slee

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