A. adj.
1. a. Having the faculty of reasoning; endowed with reason. (Freq. in rational being, creature.)
1398 TREVISA Barth. De P.R. III. xiii. (1495) 56 The soule racional, in that he vsyth contemplacion, he hyghte speculativus. 1547 BOORDE Brev. Health §321 The racionall sences consisteth in reason, the whiche doth make a man or woman a reasonable beaste. 1615 CROOKE Body of Man 432 We determine that the Braine is the Pallace of the Rationall Soule. a1641 BP. R. MONTAGU Acts & Mon. (1642) 409 Other bodies, not onely of rationall creatures, men and women, but also of irrational, birds and beasts. 1783 COWPER Let. 29 Sept., We are rational: but we are animal too. 1848 DICKENS Dombey ii, If you're a rational being, don't make such ridiculous excuses. 1908 Jrnl. Abnormal Psychol. III. 166 Everyone feels that as a rational creature he must be able to give a connected..account of himself. 1975 J. PLAMENATZ K. Marx's Philos. Man i. 17 He always speaks of man as a self-conscious, rational, active being who can make choices and can initiate change deliberately.
b. Exercising (or able to exercise) one's reason in a proper manner; having sound judgement; sensible, sane.
1632 B. JONSON Magnetick Lady III. v, You are one O' the deepest Politiques I ever met, And the most subtily rationall. 1641 H. L'ESTRANGE God's Sabbath 34 Our most Rationall adversaries begin to reel towards us. 1712 E. COOKE Voy. S. Sea 239 They were told by a good rational Indian Woman [etc.]. 1791 BURKE App. Whigs Wks. 1842 I. 535 Rational and experienced men tolerably well know,..how to distinguish between true and false liberty. 1809 Med. Jrnl. XXI. 216 Frequent restlessness and delirium, yet at times he is rational and patient. 1835 LYTTON Rienzi I. vii, Our rational and sober-minded islanders. 1856 C. BRONTË Professor xix, The man of regular life and rational mind never despairs.
c. Med. Applied to an ancient class of physicians, who deduced their treatment of cases from general principles. (Opp. to EMPIRICAL.) rational psychology, psychological science: psychology, or the science of mind, as studied by deduction from general principles, and distinguished from an empirical approach. Now Obs.
1541 COPLAND Galyen's Terap. Eiijb, Seynge that none Emperyke, nor racyonall hath so wryten before. 1654 R. WHITLOCK Zootomia 123 [They] are ready enough to slander the rationall Physitian. 1727-41 CHAMBERS Cycl. s.v. Physician, The ancients distinguished their physicians into various classes, or sects:{em}as Rational Physicians [etc.]. 1817 COLERIDGE Biog. Lit. I. ix. 139 These delusions were such, as might be anticipated..from his ignorance of rational psychology. 1837 WHEWELL Hist. Induct. Sc. IV. i. §5 That medical sect which was termed the Empirical, in contradistinction to the rational and methodical sects. 1849 L. P. HICKOK Rational Psychol. 21 Those a priori conditions which give the necessary and universal laws to experience, and by which intelligence itself is alone made intelligible, are the elements for a higher Psychological Science which we term Rational. 1861 J. S. MILL Let. in A. Bain John Stuart Mill (1882) iv. 118 It will enable me..to do the kind of service which I am capable of to rational psychology. 1892 W. JAMES Coll. Ess. & Rev. (1920) xx. 321 We certainly need something more radical than the old division into 'rational' and 'empirical' psychology, both to be treated by the same writer between the covers of the same book.
d. Rational Christians: Such as claim superior rationality for their own form of Christianity.
A sect was registered under this name in 1876.
1750 MASSON Contin. True Rationalist xii. 155 This is..what shews me how convincing your Reasons are to determine me for the Establishment of a Society of Rational Christians.
2. a. Of, pertaining or relating to, reason.
Chiefly in rational faculty, nature, power, etc. Also {dag}rational philosophy, mental philosophy.
a1601 NORTH Plutarch (1612) 1190 Morall Philosophie was his chiefest end: for the rationall, the naturall, and Mathematickes..were but simple pastimes in comparison of the other. 1614 C. BROOKE Rich. III, Poems (1872) 125 My aspick flatterie, That shed such venome in my rationall powre. 1675 BARCLAY Apol. Quakers IV. iii. 102 As he is a meer Man, he differs no otherwise from Beasts, than by the Rational Property. 1748 CHESTERFIELD Lett. (1792) II. 61 Philosophy, rational logic, rhetoric [etc.]. 1788 REID Aristotle's Logic vi. §1. 126 Our rational faculty is the gift of God. a1882 T. H. GREEN Proleg. Ethics §207 The consciousness of unfulfilled possibilities of the rational nature common to all men.
{dag}b. Existing (only) in the mind. (Opposed to REAL.) Obs.
1628 T. SPENCER Logick 104 Such things haue a being in our vnderstanding, and that is enough to make them rationall beings. 1677 GALE Crt. Gentiles IV. Proem. 6 These second Notions are not Real, but only Mental or Rational Beings, framed out of Real Beings.
3. a. Based on, derived from, reason or reasoning.
1531 ELYOT Gov. III. xxvi, That parte of phisike called rationall, wherby is declared the faculties or powers of the body, the causis, accidentes, and tokens of sikenessis. 1649 MILTON Eikon. vi. 56 He confesses a rational sovrantie of soule, and freedom of will in every man. 1701 NORRIS Ideal World I. iv. 218 Faith is a rational assent, or an assent founded on reason, tho' not the reason of the thing believed. 1785 REID Intell. Powers 608 Of tastes that are natural, there are some that may be called rational, others that are merely animal. 1885 J. MARTINEAU Types Eth. Th. (ed. 2) I. I. xi. §8. 212 Any..instance of rational apprehension, e.g. our knowledge that the surface of a sphere is equal to the area of a circle of twice its diameter.
b. spec. in Chem. and Med. (see quots.).
1850 DAUBENY Atomic The. ix. (ed. 2) 297 By rational, in contradistinction to empirical, formulæ, we mean expressions of the manner in which the respective atoms are combined or grouped together, and not merely of the number of atoms of each of the ingredients present. 1897 Allbutt's Syst. Med. IV. 275 Physical are more important than rational signs in establishing the diagnosis of cyst of the pancreas.
c. rational mechanics: mechanics as deduced logically from first principles.
[1687 NEWTON Philosophiæ Naturalis Principia Mathematica p. v, Mechanicam vero duplicem Veteres constituerunt: Rationalem quæ per Demonstrationes accurate procedit, & Practicam. Ibid., Quo sensu Mechanica rationalis erit Scientia Motuum qui ex viribus quibuscunq; resultant, & virium quæ ad motus quoscunq; requiruntur, accurate proposita ac demonstrata. 1729 A. MOTTE tr. Ibid. I. p. vii, The ancients considered Mechanics in a twofold respect; as rational, which proceeds accurately by demonstration, and practical.] Ibid. p. ix, In this sense Rational Mechanics will be the science of motions resulting from any forces whatsoever and of the forces required to produce any motions, accurately proposed and demonstrated. 1902 J. W. GIBBS Elem. Princ. Statistical Mech. p. ix, Nothing will more conduce to the clear apprehension of the relation of thermodynamics to rational mechanics..than the study of the fundamental notions and principles of that department of mechanics to which thermodynamics is especially related. 1928 R. DE VILLAMIL Rational Mech. p. vi, I have been asked: Why I call this a book on 'Rational Mechanics'? and Do I not consider all Mechanics as being 'Rational'? 1952 Jrnl. Rational Mech. & Anal. I. p. ii, The Journal of Rational Mechanics & Analysis nourishes mathematics with physical applications, aiming especially to close the rift between 'pure' and 'applied' mathematics and to foster the discipline of mechanics as a deductive, mathematical science in the classical tradition. 1958 Science 4 Apr. 729/1 In the United States..rational mechanics is not a recognized science. Indeed, there are some who disbelieve in its existence. 1977 C. TRUESDELL First Course Rational Continuum Mech. i. 4 Rational Mechanics is the part of mathematics that provides and develops logical models for the enforced changes of position and shape which we see everyday things suffer.
4. a. Agreeable to reason; reasonable, sensible; not foolish, absurd, or extravagant.
1635 E. PAGITT Christianogr. I. iii. (1636) 123 We offer unto thee, this rationall and unbloody worship. 1654-66 EARL OF ORRERY Parthen. (1676) 750 He might decline that Assistance, in which he had his Rationallest hopes. 1691 LOCKE Money Wks. 1727 II. 92 What Mr. Lowndes says about Gold Coins,..appears to me highly rational. 1771 Junius Lett. lxiv. 325 [He] will..concur in any rational plan that may provide for the liberty of the individual. 1804 ABERNETHY Surg. Obs. 176 On the following morning..his answers were rational. 1879 G. C. HARLAN Eyesight viii. 104 All the organs of the body are better for moderate and rational use.
b. rational dress: A form of dress for women, proposed in the late 19th c. as more sensible than that in general use, usually denoting the use of knickerbockers in place of a skirt, esp. for cycling. (Also attrib.) So rational costume, etc.
1883 Catal. Rational Dress Exhib. Pref., The Rational Dress Exhibition is intended to stimulate both the supply and the demand for good dress. 1888 Rational Dress Society's Gaz. No. 2 This is the time when rational dress principles will have more weight. 1899 Cycl. Tour. Club Gaz. Apr. 221 If..senior churchwardens protest against rational costume.
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