RATIONAL: — That which belongs to reason (v.) or is in conformity with II. In this sense, rational is said of demonstration (v.), deduction (v.), as well as the very activity of reason consisting in combining concepts and propositions.
Judging well is also a rational act (Descartes, Disc. de la mét., I, 1), that is, the act that knows how to distinguish the true from the false, the good from the evil, etc. Likewise, natural truth is called rational to distinguish it from the superrational revealed truth (v. RATIONALISM); and rational is also the system of a priori principles, logically formulated, whose origin and value are independent of sensible experience. Hegel (v.), who makes the concept (v.) the essence of things, identifies the real with the rational: “whatever is rational is real; and whatever is real is rational” (Filos. del diritto, pref.). There are other particular meanings as well: for example, in the sense of “good method” (a “rational education”), “rational distribution” of the parts of a subject, etc. Mathematicians speak of “rational number”; that is, one that can be expressed as the ratio of two integers; and physicists speak of “rational mechanics”; that is, mechanics constructed by a purely deductive method starting from the notions of mass, force, and inertia.
Cournot opposes logical order and rational order; the former, according to him, is linear and discursive, the latter synthetic and intuitive; logical order determines assent (v.) without showing the true reasons of things; rational order, instead, connects truths to their natural principle and enlightens the mind. As is well known, modern rationalism and Kant oppose the rational to the empirical.