A cause:
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.
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.
I reasoned the matter with my friend.
To support with reasons, as a request.
To persuade by reasoning or argument.
to reason one into a belief; to reason one out of his plan
(with down) To overcome or conquer by adducing reasons.
to reason down a passion
(usually with out) To find by logical process; to explain or justify by reason or argument.
to reason out the causes of the librations of the moon