logic (n.) Look up logic at Dictionary.com
mid-14c., "branch of philosophy that treats of forms of thinking," from Old French logique (13c.), from Latin (ars) logica, from Greek logike (techne) "reasoning (art)," from fem. of logikos "pertaining to speaking or reasoning," from logos "reason, idea, word" (see logos). Meaning "logical argumentation" is from c.1600.