1911 Encyclopædia Britannica/Deduction

DEDUCTION (from Lat. deducere, to take or lead from or out of, derive), a term used in common parlance for the process of taking away from, or subtracting (as in mathematics), and specially for the argumentative process of arriving at a conclusion from evidence, i.e. for any kind of inference.^[1] In this sense it includes both arguments from particular facts and those from general laws to particular cases. In logic it is generally used in contradiction to “induction” for a kind of mediate inference, in which a conclusion (often itself called the deduction) is regarded as following necessarily under certain fixed laws from premises. This, the most common, form of deduction is the syllogism (q.v.; see also Logic), which consists in taking a general principle and deriving from it facts which are necessarily involved in it. This use of deduction is of comparatively modern origin; it was originally used as the equivalent of Aristotle’s ἀπαγωγή (see Prior Analytics, B xxv.). The modern use of deduction is practically identical with the Aristotelian συλλογισμός.

1. Two forms of the verb are used, “deduce” and “deduct”; originally synonymous, they are now distinguished, “deduce” being confined to arguments, “deduct” to quantities.