deduction

deduction in logic , form of inference such that the conclusion must be true if the premises are true. For example, if we know that all men have two legs and that John is a man, it is then logical to deduce that John has two legs. Logicians contrast deduction with induction , in which the conclusion might be false even when the premises are true. Deduction has to do with necessity; induction has to do with probability. The famous Aristotelian syllogism is one species of deductive reasoning, which was greatly extended by the development of symbolic logic .

Bibliography: See R. J. Ackermann, Modern Deductive Logic (1971); P. J. Hurley A Concise Introduction to Logic (1985).

deduction, deductive The use of logical rules to arrive at a set of premisses from which certain conclusions must follow. Deduction begins with theory, moves to hypotheses derived from the theory, and then tests hypotheses via prediction and observations. This approach to testing and theory is often referred to as the hypothetico-deductive method, and since it emphasizes hypotheses, prediction, and testing, is sometimes held to be the method par excellence of science. See also INDUCTION.

deduction A formal method of logical inference. Deduction is the process of applying one or more inference rules to a given set of facts (known as axioms) and inferring new facts. Unlike the other methods of inference, abduction and induction, deduction produces logically sound results, i.e. involves no uncertainty.