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.n. A quiddity; a universal; a. nature.n. Eccles.:n. The breastplate of the Jewish high-priest.n. 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.n. In mathematics, a rational number.n. One who is a believer in so-called ‘rational’ reforms, as in dress or food.
