Etymology From Middle English resoun, reson, from Anglo-Norman raisun (Old French raison), from Latin ratiō, from ratus, past participle of reor (“reckon”), ultimately from Proto-Indo-European *h₂reh₁- (“to think”), reanalysed root of *h₂er- (“to put together”). Displaced native Middle English reden (found in compounds), from Old English rǣden (“condition, stipulation, calculation, direction”), from the same Proto-Indo-European source (compare West Frisian reden (“reason”), Dutch reden (“reason”)). Doublet of ration and ratio.
That which causes something: an efficient cause, a proximate cause.
The reason this tree fell is that it had rotted.
There is a reason why so many should be symmetrical: The selective advantage in a symmetrical complex is enjoyed by all the subunits[…]1996, Daniel Clement Dennett, Darwin’s Dangerous Idea: Evolution and the Meanings of Life, page 198:
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A motive for an action or a determination.
He made reason with his boss about taking a day off.
The reason I robbed the bank was that I needed the money.
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If you don't give me a reason to go with you, I won't.
This is the reason why he proposes to offer a libation, to atone for the abuse of the day by their diversions.1806, Anonymous, Select Notes to Book XXI, in, Alexander Pope, translator, The Odyssey of Homer, volume 6 (London, F.J. du Roveray), page 37
Ralph Touchett, for reasons best known to himself, had seen fit to say that Gilbert Osmond was not a good fellow[…]1908, Henry James, chapter 10, in The Portrait of a Lady (The Novels and Tales of Henry James), New York edition, volume (please specify |volume=I or II), Boston, Mass.; New York, N.Y.: Charles Scribner’s Sons, →OCLC; republished as The Portrait of a Lady (EBook #283), United States: Project Gutenberg, 1 September 2001:
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An excuse: a thought or a consideration offered in support of a determination or an opinion; that which is offered or accepted as an explanation.
I have forgotten the reason he gave for not travelling by air. I felt sure that it was not the correct reason, and that he suffered from a heart trouble which he kept to himself.1966, Graham Greene, The Comedians, Penguin Classics, →ISBN, page 14:
Rational thinking (or the capacity for it); the cognitive faculties, collectively, of conception, judgment, deduction and intuition.
Mankind should develop reason above all other virtues.
The tremendous tragedy in which he had been involved - it was evident he was a fugitive from Weybridge - had driven him to the very verge of his reason.1898, H.G. Wells, The War of the Worlds, London: William Heinemann, page 113:
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And the specific distinction between man and beast is now, strictly speaking, no longer reason (the lumen naturale of the human animal) but science[…]1970, Hannah Arendt, On Violence, →ISBN, page 62:
The [Isaac] Newton that emerges from the [unpublished] manuscripts is far from the popular image of a rational practitioner of cold and pure reason. The architect of modern science was himself not very modern. He was obsessed with alchemy.2014 June 21, “Magician’s brain”, in The Economist, volume 411, number 8892:
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Obsolete Something reasonable, in accordance with thought; justice.
16th century Edmund Spenser, Lines on his Promised Pension I was promised, on a time, To have reason for my rhyme.
[I]f two Quantities repreſented by the Numbers 20 and 4 be compared, by dividing the Antecedent 20 by the Conſequent 4, the Quotient is 5; but inverting the Terms, by dividing 4 by 20 the Quotient is #92;tfrac#123;4#125;#123;20#125;#61;#92;tfrac#123;1#125;#123;5#125;. By which Quotients are declared the Geometrical Reaſons of the propoſed Quantities, becauſe if the Quotient found be multiplied by the Conſequent, the Product is equal to the Antecedent; for in the former Compariſon 5#92;times4#61;20, in the latter #92;tfrac#123;1#125;#123;5#125;#92;times20#61;4; as Things again are referred to Equality.1734, Isaac Barrow, “Lecture XVII. Of the Names and Diversities of the Twofold Kind of Reason or Proportion, viz. Arithmetical and Geometrical”, in John Kirkby, transl., The Usefulness of Mathematical Learning Explained and Demonstrated: Being Mathematical Lectures Read in the Publick Schools at the University of Cambridge. […], London: […] Stephen Austen, […], →OCLC, pages 323–324:
Etymology From Middle English resoun, reson, from Anglo-Norman raisun (Old French raison), from Latin ratiō, from ratus, past participle of reor (“reckon”), ultimately from Proto-Indo-European *h₂reh₁- (“to think”), reanalysed root of *h₂er- (“to put together”). Displaced native Middle English reden (found in compounds), from Old English rǣden (“condition, stipulation, calculation, direction”), from the same Proto-Indo-European source (compare West Frisian reden (“reason”), Dutch reden (“reason”)). Doublet of ration and ratio.
To deduce or come to a conclusion by being rational.
"I had," said he, "come to an entirely erroneous conclusion which shows, my dear Watson, how dangerous it always is to reason from insufficient data. […]"1892, Arthur Conan Doyle, The Adventure of the Speckled Band:
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To perform a process of deduction or of induction, in order to convince or to confute; to argue.
Still my spirit was not broken. I indulged the anticipation of escape, and that speedily. It was impossible, I reasoned, that men could be so unjust as to detain me as a slave, when the truth of my case was known.1853, Solomon Northup, chapter III, in [David Wilson], editor, Twelve Years a Slave. […], London: Sampson Low, Son & Co.; Auburn, N.Y.: Derby and Miller, →OCLC, page 47:
“All right, Dad – I did follow you. But only because I was worried about you.” “Worried about me? I was worried about you! Hanging on to the roof of a speeding car! Are you nuts?” “It wasn’t moving when I climbed on to it,” reasoned the boy.2017, David Walliams [pseudonym; David Edward Williams], Bad Dad, London: HarperCollins Children’s Books, →ISBN:
Ambitransitive To arrange and present the reasons for or against; to examine or discuss by arguments; to debate or discuss.
I reasoned the matter with my friend.
The talk was mainly between Aleck and Murdie, the others crowding eagerly about and putting in a word as they could. Murdie was reasoning good-humoredly, Aleck replying fiercely.1901, Ralph Connor, chapter 9, in The Man from Glengarry:
to reason one into a belief; to reason one out of his plan
That she was not immediately ready, Emma did suspect to arise from the state of her nerves; she had not yet possessed the instrument long enough to touch it without emotion; she must reason herself into the power of performance; and Emma could not but pity such feelings, whatever their origin, and could not but resolve never to expose them to her neighbour again.1815 December (indicated as 1816), [Jane Austen], chapter 10, in Emma: […], volume (please specify |volume=I to III), London: […] [Charles Roworth and James Moyes] for John Murray, →OCLC:
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With down To overcome or conquer by adducing reasons.
to reason down a passion
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Usually, With out To find by logical process; to explain or justify by reason or argument.
to reason out the causes of the librations of the moon
Etymology From Middle English reason, reson, resen, rasen, from Old English ræsn (“beam, rafter, ceiling, wall panel”), probably from Proto-West Germanic *raʀn (“house”), from Proto-Germanic *razną (“house, dwelling”), from Proto-Indo-European *h₁erh₁- (“to rest”).