1. The study of the principles of reasoning, especially of the structure of propositions as distinguished from their content and of method and validity in deductive reasoning.
2. 1. A system of reasoning: Aristotle's logic.
   2. A mode of reasoning: By that logic, we should sell the company tomorrow.
   3. The formal, guiding principles of a discipline, school, or science.
3. Valid reasoning: Your paper lacks the logic to prove your thesis.
4. The relationship between elements and between an element and the whole in a set of objects, individuals, principles, or events: There's a certain logic to the motion of rush-hour traffic.
5. Computer Science.
   1. The nonarithmetic operations performed by a computer, such as sorting, comparing, and matching, that involve yes-no decisions.
   2. Computer circuitry.
   3. Graphic representation of computer circuitry.

[Middle English, from Old French logique, from Latin logica, from Greek logikē (tekhnē), (art) of reasoning, logic, feminine of logikos, of reasoning, from logos, reason.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.