A cause:
Rational thinking (or the capacity for it); the cognitive faculties, collectively, of conception, judgment, deduction and intuition.
Something reasonable, in accordance with thought; justice.
Ratio; proportion.
To deduce or come to a conclusion by being rational
To perform a process of deduction or of induction, in order to convince or to confute; to argue.
To converse; to compare opinions.
To arrange and present the reasons for or against; to examine or discuss by arguments; to debate or discuss.
To support with reasons, as a request.
To persuade by reasoning or argument.
(with down) To overcome or conquer by adducing reasons.
(usually with out) To find by logical process; to explain or justify by reason or argument.