Word of the Day – Tuesday, January 24th



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Deduce; also, to elicit, or bring out
Common clues: Elicit; Extract;
Infer; Draw out; Figure out; Bring out; Draw forth; Develop; Construe; Draw out something latent
Crossword puzzle frequency: 2 times a year
Watson tries deduction

Deductive reasoning is reasoning whose conclusions are intended to necessarily follow from its premises. It is more commonly understood as the type of reasoning that proceeds from general principles or premises to derive particulars, although this is a less precise understanding. Deductive reasoning "merely" reveals the implications of propositions, laws, or general principles, so that, like some philosophers claim, it does not add to truth.


Deductive reasoning was developed by Aristotle, Thales, Pythagoras, and other Greek philosophers of the Classical Period (600 to 300 B.C.). Aristotle, for example, relates a story of how Thales used his skills to deduce that the next season's olive crop would be a very large one. He therefore bought all the olive presses and made a fortune when the bumper olive crop did indeed arrive.

Deductive reasoning is dependent on its premises. That is, a false premise can possibly lead to a false result, and inconclusive premises will also yield an inconclusive conclusion.

Alternative to deductive reasoning is inductive reasoning. The basic difference between the two can be summarized in the deductive dynamic of logically progressing from general evidence to a particular truth or conclusion; whereas with induction the logical dynamic is precisely the reverse. Inductive reasoning starts with a particular observation that is believed to be a demonstrative model for a truth or principle that is assumed to apply generally.

Deductive reasoning applies general principles to reach specific conclusions, whereas inductive reasoning examines specific information, perhaps many pieces of specific information, to impute a general principle. By thinking about phenomena such as how apples fall and how the planets move, Isaac Newton induced his theory of gravity. In the 19th century, Adams and LeVerrier applied Newton's theory (general principle) to deduce the existence, mass, position, and orbit of Neptune (specific conclusions) from perturbations in the observed orbit of Uranus (specific data).

Deductive reasoning is supported by deductive logic (which is not quite the same thing).

For example:

All apples are fruit.

All fruits grow on trees.

Therefore all apples grow on trees.


All apples are fruit.

Some apples are red.

Therefore some fruit is red.

Intuitively, one might deny the major premise and hence the conclusion; yet anyone accepting the premises accepts the conclusion.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Deductive reasoning"