from The American Heritage® Dictionary of the English Language, 5th Edition.

  • adjective Having or exercising the ability to reason. synonym: logical.
  • adjective Consistent with or based on reason or good judgment; logical or sensible.
  • adjective Of sound mind; sane.
  • adjective Mathematics Capable of being expressed as a quotient of integers.
  • noun A rational number.

from The Century Dictionary.

  • noun In mathematics, a rational number.
  • noun One who is a believer in so-called ‘rational’ reforms, as in dress or food.
  • Of, pertaining to, or springing from the reason, in the sense of the highest faculty of cognition.
  • Endowed with reason, in the sense of that faculty which distinguishes man from the brutes: as, man is a rational animal.
  • Conformable to the precepts of reason, especially of the practical reason; reasonable; wise.
  • In arithmetic and algebra:
  • Expressible in finite terms: applied to expressions in which no extraction of a root is left, or, at least, none such indicated which cannot be actually performed by known processes.
  • In Euclid's “Elements” and commentaries, etc., on that work, commensurable with a given line.
  • In ancient prosody, capable of measurement in terms of the metrical unit (semeion or mora).
  • The composition of elements which only differ as viewed by the mind, and not as they exist, as the composition of essence and existence, of being and relation, etc.
  • The union of several objects so far as they are brought together into or under one concept.
  • The limits of rational knowledge.
  • Knowledge springing directly or indirectly from reason, and not from experience.
  • Synonyms Rational, Reasonable, sensible, enlightened, discreet, intelligent, sane, sound. The first two words are somewhat different, according as they refer to persons or things. As to persons, rational is the more speculative, reasonable the more practical term; rational means possessing the faculty of reason, while reasonable means exercising reason in its broader sense, in opposition to unreasonable—that is, guided by prejudice, fancy, etc. In fever the patient may become irrational and give irrational answers; when he is rational he may through weakness and fretfulness make unreasonable demands of his physician. As to things, the distinction continues between the narrower and the broader senses: a rational proposition is one that might proceed from a rational mind; a reasonable proposition is one that is marked by common sense and fairness. It is irrational to look for a coal-mine in a granite-ledge; it is unreasonable to expect good work for poor pay. See absurd.
  • noun A quiddity; a universal; a. nature.
  • noun Eccles.:
  • noun The breastplate of the Jewish high-priest.
  • noun Hence— A square plate of gold, silver, or embroidery, either jeweled or enameled, formerly worn on the breast over the chasuble by bishops during the celebration of mass. Also pectoral and rationale in both senses.

from the GNU version of the Collaborative International Dictionary of English.

  • noun A rational being.
  • adjective Relating to the reason; not physical; mental.
  • adjective Having reason, or the faculty of reasoning; endowed with reason or understanding; reasoning.
  • adjective Agreeable to reason; not absurd, preposterous, extravagant, foolish, fanciful, or the like; wise; judicious
  • adjective (Chem.) Expressing the type, structure, relations, and reactions of a compound; graphic; -- said of formulæ. See under Formula.
  • adjective (Astron.) See Horizon, 2 (b).
  • adjective (Alg.) one that can be expressed without the use of a radical sign, or in exact parts of unity; -- opposed to irrational or radical quantity.
  • adjective (Med.) one elicited by the statements of the patient himself and not as the result of a physical examination.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • adjective Capable of reasoning.
  • adjective Logically sound; not contradictory or otherwise absurd.
  • adjective Healthy or balanced intellectually; exhibiting reasonableness.
  • adjective mathematics, arithmetic, number theory, not comparable Of a number, capable of being expressed as the ratio of two integers.
  • adjective mathematics, arithmetic, not comparable Of an algebraic expression, capable of being expressed as the ratio of two polynomials.
  • noun mathematics A rational number: a number that can be expressed as the quotient of two integers.
  • noun A rational being.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun an integer or a fraction
  • adjective having its source in or being guided by the intellect (as distinguished from experience or emotion)
  • adjective of or associated with or requiring the use of the mind
  • adjective capable of being expressed as a quotient of integers
  • adjective consistent with or based on or using reason


from The American Heritage® Dictionary of the English Language, 4th Edition

[Middle English racional, from Old French racionel, from Latin ratiōnālis, from ratiō, ratiōn-, reason; see reason.]

from Wiktionary, Creative Commons Attribution/Share-Alike License

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.

from Wiktionary, Creative Commons Attribution/Share-Alike License

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


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  • A rational number may be written as the quotient of two integers, that is, in the form a/b for some two integers a and b.

    Some famously irrational numbers include the square root of two, π, and e, the base of natural logarithms.

    How many rational numbers are there? Infinitely many. But only countably infinitely many: as the rationals may be set in one-to-one correspondence with the integers, the two sets have the same cardinality.

    November 16, 2007

  • In organizational sociology, rational can also mean rule-based or top-down, as opposed to personal or idiosyncratic. This usage derives from Max Weber's definition of rational-legal authority in bureaucracy; this notion is often expressed with the shorthand "rational bureaucracy" or "rational systems".

    See for example Meyer and Rowan 1977:

    "In conventional theories of organization, rational formal structure is assumed to be the most effective way to coordinate and control the complex relational networks involved in modern technical or work activities." (342)

    "As rationalized institutional rules are given in domains of work activity, formal organizations form and expand by incorporating these rules as structural elements." (345)

    January 31, 2010