n (uncountable) rational | Rational thinking (or the capacity for it; the cognitive faculty|faculties, collectively, of conception, judgment, deduction and intuition.
v (intransitive) 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.
v (intransitive) 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.
v (transitive) To arrange and present the reasons for or against; to examine or discuss by arguments; to debate or discuss.
v (transitive|usually with out) To find by logical process; to explain or justify by reason or argument.