1. noun /ˈɹiːzən/
a) a cause:
Mankind should develop reason above all other virtues.
And the specific distinction between man and beast is now, strictly speaking, no longer reason (the lumen naturale of the human animal) but science….
2. verb /ˈɹiːzən/
a) To exercise the rational faculty; to deduce inferences from premises; to perform the process of deduction or of induction; to ratiocinate; to reach conclusions by a systematic comparison of facts.
I reasoned the matter with my friend.
b) Hence: To carry on a process of deduction or of induction, in order to convince or to confute; to formulate and set forth propositions and the inferences from them; to argue.
to reason one into a belief; to reason one out of his plan
Wikipedia foundation.