logic
log.ic \'la:j-ik\ \lo--'jish-*n\ n [ME logik, fr. MF logique, fr. L logica, fr. Gk logike-], fr. fem. of logikos of reason, fr. logos reason - more at LEGEND 1a1: a science that deals with the canons and criteria of validity of infer ence and demonstration : the science of the normative formal principles of reasoning 1a2: a branch of semiotic; esp : SYNTACTICS 1a3: the formal principles of a branch of knowledge 1b: a particular mode of reasoning 1c: interrelation or sequence of facts or events when seen as inevitable or predictable 2: something that forces a decision apart from or in opposition to reason <(the ~ of war} - lo.gi.cian n
Webster's English Dictionary