irrational

irrational
irrational, unreasonable are comparable when meaning not governed or guided by reason. Both terms have been used occasionally in the sense of not having the power to reason
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nothing has a greater effect on all plants and irrational animals— Hume

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whilst his fellowman . . . must as the unreasonable beast drag on a life of labor— Southey

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Except in technical senses (as in mathematics) both words apply usually to men, their acts, utterances, feelings, policies, and demands.
Irrational may imply a lack of usual or normal mental control and powers
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the patient was irrational during the course of his fever

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but more often it suggests a lack of control or guidance by the reason, or direct conflict with reason's dictates; it therefore comes close to absurd, illogical, foolish, pre-posterous, senseless, or fantastic
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governed by an irrational fear

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irrational beliefs

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an irrational policy

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his temperamental impulse to energetic practical action . . . and the reserve, passivity, and isolation which myopia enforced, seemed to him absolutely irrationalEllis

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though normal and very intelligent in most respects Mrs. Lincoln was irrational on one subject: she could not think straight in matters that pertained to money— R. P. Randall

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Unreasonable implies guidance or control by some force (as self-will, passion, ambition, greed, or stubbornness) which makes one deficient in judgment or good sense. As applied to one's acts or utterances, it suggests lack of justification by reason; the term therefore comes close to inequitable, immoderate, excessive, unfair, or extravagant
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you will not be so unreasonable as to send your child out in this storm

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his demands are unreasonable

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obstinate and unreasonable pertinacity

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an unreasonable price for beef

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the earnings . . . were found materially in excess of a fair return, and the general level of their rates was found unjust and unreasonable—J. C. Nelson

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it is a little unreasonable to find fault with his maxims because they do not apply to all times and places— A. M. Young

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Analogous words: absurd, preposterous, *foolish, silly: fatuous, asinine, *simple: crazy, demented, mad, *insane
Antonyms: rational
Contrasted words: reasonable (see RATIONAL): *wise, judicious, sage, sapient, prudent, sane, sensible: *logical

New Dictionary of Synonyms. 2014.

Synonyms:

Look at other dictionaries:

  • Irrational — may refer to: *Irrationality *Irrational rhythm, *Irrational exuberance *Irrational GamesIn mathematics: *Irrational number *Proof that e is irrational *Proof that pi; is irrational *Quadratic irrational *List of integrals of irrational… …   Wikipedia

  • irrational — ir·ra·tio·nal /ir ra shə nəl/ adj: not rational: as a: not governed by reason, mental clarity, or understanding b: not governed by a fair consideration of facts or evidence; broadly: arbitrary an irrational decision to deny the permit… …   Law dictionary

  • irrational — [i rash′ə nəl] adj. [ME < L irrationalis: see IN 2 & RATIONAL] 1. lacking the power to reason 2. contrary to reason; senseless; unreasonable; absurd 3. Math. designating a real number not expressible as an integer or as a quotient of two… …   English World dictionary

  • irrational — ir*ra tion*al ([i^]r*r[a^]sh [u^]n*al), a. [L. irrationalis: cf. F. irrationnel. See {In } not, and {Rational}.] [1913 Webster] 1. Not rational; void of reason or understanding; as, brutes are irrational animals. [1913 Webster] 2. Not according… …   The Collaborative International Dictionary of English

  • irrational — Adj. (Mittelstufe) nicht von der Vernunft geleitet, unvernünftig Beispiel: Die Situation wirkt ziemlich irrational. Kollokation: sich irrational verhalten …   Extremes Deutsch

  • Irrational — (v. lat., fr. Irraisonabel), 1) vernunftwidrig; 2) unüberlegt; 3) (Math.), ein Verhältnißbegriff für Größen, deren eine nicht aus Theilen der anderen zusammengesetzt werden kann, z.B. die Diagonale eines Quadrats od. Cubus in Beziehung auf deren… …   Pierer's Universal-Lexikon

  • Irrationāl — (lat., irrationell), vernunftwidrig, unvernünftig; in der Mathematik Bezeichnung für eine Zahl, die zur Einheit inkommensurabel ist (s. Größe, S. 421), deren Wert man daher nicht völlig genau, sondern nur annähernd (durch einen unendlichen, nicht …   Meyers Großes Konversations-Lexikon

  • Irrational — Irrational, Bezeichnung für mehrdeutige algebraische Funktionen …   Lexikon der gesamten Technik

  • Irrational — Irrationāl (lat.), vernunftwidrig; in der Mathematik Bezeichnung von Zahlgrößen, die sich nicht durch ganze Zahlen oder Brüche, sondern nur annähernd (durch unendliche Dezimalbrüche) ausdrücken lassen, wie z.B. die Wurzel ganzer Zahlen, die nicht …   Kleines Konversations-Lexikon

  • Irrational — Irrational, lat. deutsch, vernunftwidrig; I.ismus, I.ität, Vernunftwidrigkeit. In der Mathematik heißen diejenigen Größen i.e, welche in ihren Theilen nicht durch einander zusammengesetzt werden können; bei den Zahlen diejenigen, welche sich… …   Herders Conversations-Lexikon

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