reasonyoudaoicibaDictYouDict[reason 词源字典]
reason: [13] Reason, together with rational, represent in English the ‘thinking’ aspects of the Latin verb rērī (it also meant ‘calculate’, and in that guise has given English rate, ration, etc). From it was derived the noun ratiō ‘thinking, calculation’ (source of English ratio and the rest). This spawned a Vulgar Latin variant *ratiōne, which passed into Old French as reisun – whence English reason.
=> rate, ratio, ration[reason etymology, reason origin, 英语词源]
reason (n.)youdaoicibaDictYouDict
c. 1200, "intellectual faculty that adopts actions to ends," also "statement in an argument, statement of explanation or justification," from Anglo-French resoun, Old French raison "course; matter; subject; language, speech; thought, opinion," 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" (source of Old English rædan "to advise;" see read (v.)).

Meaning "sanity; degree of intelligence that distinguishes men from brutes" is recorded from late 13c. Sense of "grounds for action, motive, cause of an event" is from c. 1300. Middle English sense of "meaning, signification" (early 14c.) is in the phrase rhyme or reason. 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.)youdaoicibaDictYouDict
early 14c., resunmen, "to question (someone)," also "to challenge," from Old French raisoner "speak, discuss; argue; address; speak to," from Late Latin rationare "to discourse," from ratio (see reason (n.)). Intransitive sense of "to think in a logical manner" is from 1590s; transitive sense of "employ reasoning (with someone)" is from 1847. Related: Reasoned; reasoning.