Deduction

Deduction, in logic, the form of reasoning by which a specific conclusion is inferred from one or more premises. In valid deductive reasoning, the conclusion must be true if all the premises are true. Thus, if it is agreed that all human beings have one head and two arms, and that Bertha is a human being, then it can logically be concluded that Bertha must have one head and two arms. This is an example of a syllogism, an argument in which two premises are given and a logical conclusion is deduced from them. Deduction is often expressed in the form of syllogisms.

See also Induction.