noun

1. A cause:

2. Rational thinking (or the capacity for it); the cognitive faculties, collectively, of conception, judgment, deduction and intuition.

   “Mankind should develop reason above all other virtues.”

3. Something reasonable, in accordance with thought; justice.

Synonyms: motive, rationale, cause, excuse

verb

1. To deduce or come to a conclusion by being rational

2. To perform a process of deduction or of induction, in order to convince or to confute; to argue.

3. To converse; to compare opinions.