'Reason,' 'ratio,' 'ration,' and 'rate' areallthe same Latin word — 'ratio' (reckoning). Math became thought.
Definition
The power of the mind to think and understand in a logical way; a cause, explanation, or justification for an action or event.
The Full Story
Latin13th centurywell-attested
From OldFrench 'raison' (reason, cause, thought, explanation), from Latin 'ratiō' (a reckoning, a calculation, an account, reason, understanding, judgment), from 'ratus,' past participle of 'rērī' (to reckon, to think, to calculate, to suppose), from PIE *h₂reh₁- (to reason, to count, to fit together). The original meaning was mathematical — counting, reckoning, accounting — and it broadened gradually to encompass any form of orderly thought, logical argument, or cause-and-effect explanation. This semantic expansion from 'counting' to 'thinking' reveals how early
'ratio' (a calculated proportion), 'ration' (a measured share), 'rate' (a calculated amount), and 'ratify' (to make an account firm). The French phrase 'raison d'être' (reason for being) preserves the philosophical depth the
-divine status as the supreme human faculty. German took a different path: 'Vernunft' (reason) derives from 'vernehmen' (to perceive), grounding reason in sensory experience rather than calculation. Key roots: ratiō (Latin: "reckoning, calculation, reason"), *h₂reh₁- (Proto-Indo-European: "to reason, to count").