- reason (n.)
- early 13c., "statement in an argument," also "intellectual faculty that adopts actions to ends," from Anglo-French resoun, Old French raison, from Latin rationem (nominative ratio) "reckoning, understanding, motive, cause," from ratus, past participle of reri "to reckon, think," from PIE root *re(i)- "to reason, count" (cf. Old English rædan "to advise; see read).
Meaning "sanity" is recorded from, late 14c. Phrase it stands to reason is from 1630s. Age of Reason "the Enlightenment" is first recorded 1794, as the title of Tom Paine's book. - reason (v.)
- c.1400, "to question (someone)," also "to challenge," from Old French raisoner, from Late Latin rationare "to discourse," from ratio (see reason (n.)). Sense of "employ reasoning (with someone)" is from 1847, and that of "to think in a logical manner" is from 1590s. Related: Reasoned; reasoning.