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Alternative forms[edit]


  • enPR: ră'sh(ə)nəl, IPA(key): /ˈræʃ(ə)nəl/
  • (file)

Etymology 1[edit]

From Old French rationel, rational, from Latin rationalis ‎(of or belonging to reason, rational, reasonable), from ratio ‎(reason)


rational ‎(comparative more rational, superlative most rational)

  1. Capable of reasoning.
    Man is a rational creature.
    • 2001, Mark Sainsbury, chapter 1, Logical Forms — An Introduction to Philosophical Logic, 2nd edition, Blackwell Publishing, ISBN 978-0-63121-679-7, §7, page 32:
      The utility of valid arguments is a monument to our frailty: to the fact that we are not completely rational beings.
  2. Logically sound; not contradictory or otherwise absurd.
    His statements were quite rational.
  3. (of a person or personal characteristics) Healthy or balanced intellectually; exhibiting reasonableness.
    rational conduct
    • 2014 June 21, “Magician’s brain”, The Economist, volume 411, number 8892: 
      The [Isaac] Newton that emerges from the [unpublished] manuscripts is far from the popular image of a rational practitioner of cold and pure reason.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.
  4. (mathematics, arithmetic, number theory, not comparable) Of a number, capable of being expressed as the ratio of two integers.
    ¾ is a rational number, but √2 is an irrational number.
  5. (mathematics, arithmetic, not comparable) Of an algebraic expression, capable of being expressed as the ratio of two polynomials.
  6. (chemistry) Expressing the type, structure, relations, and reactions of a compound; graphic; said of formulae.
Related terms[edit]

Etymology 2[edit]

From Old French rational, from Medieval Latin rationale ‎(a pontifical stole, a pallium, an ornament worn over the chasuble), neuter of Latin rationalis ‎(rational), for which see the first etymology.


rational ‎(plural rationals)

  1. (mathematics) A rational number: a number that can be expressed as the quotient of two integers.
    The quotient of two rationals is again a rational.
  2. A rational being.
    (Can we find and add a quotation of Young to this entry?)