rea·son

– noun
1. a basis or cause, as for some belief, action, fact, event, etc.
2. a statement presented in justification or explanation of a belief or action.
3. the mental powers concerned with forming conclusions, judgments, or inferences.
4. sound judgment; good sense.
5. normal or sound powers of mind; sanity.
6. a premise of an argument.
7. a. the faculty or power of acquiring intellectual knowledge, either by direct understanding of first principles or by argument.
b. the power of intelligent and dispassionate thought, or of conduct influenced by such thought.
c. the faculty by which the ideas of pure reason are created.
– verb
8. to think or argue in a logical manner.
9. to form conclusions, judgments, or inferences from facts or premises.
10. to urge reasons which should determine belief or action.
11. to think through logically, as a problem.
12. to conclude or infer.
13. to convince, persuade, etc.