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. a system of reasoning: Aristotle's logic.
3. a train of thought.
4. the formal, guiding principles of a discipline, school or science.
5. the relationship between elements and between an element and the whole in a set of objects, individuals, principals, or events: There's a certain logic to the motion of rush-hour traffic.