REASON, in philosophy, the faculty or process of drawing logical inferences. Thus we speak of man as essentially a rational animal, it being implied that man differs from all other animals in that he can consciously draw inferences from premises. It is, however, exceedingly difficult in this respect to draw an abso lute distinction between men and animals, observation of which undoubtedly suggests that the latter have a certain power of making inferences. Between the higher animals and the lower types of mankind the distinction is so hard to draw that many psychologists argue that the difference is one of degree rather than of kind (see INSTINCT IN MAN). There is little doubt, how ever, that inference by man differs from that of the brute creation in respect of self-consciousness, and, though there can be no doubt that some animals dream, it is difficult to find evidence for the presence of ideas in the minds of the lower animals. In the nature of the case satisfactory conclusions as to the rationality which may be predicated of animals are impossible.
The term "reason" is also used in several narrower senses. Thus reason is opposed to sensation, perception, feeling, desire, as the faculty (the existence of which is denied by empiricists) by which fundamental truths are intuitively apprehended. These fundamental truths are the causes or "reasons" (apxat) of all derivative facts. With Kant, reason (Vernunft) is the power of synthesizing into unity, by means of comprehensive principles, the concepts provided by the intellect (Verstand). The reason which gives a priori principles Kant calls "Pure Reason," as distin guished from the "Practical Reason" which is specially concerned with the performance of actions. In formal logic the drawing of
inferences (frequently called "ratiocination," from Lat. ratiocinari, to use the reasoning faculty) is classified from Aristotle down wards as deductive (from generals to particulars) and inductive (from particulars to generals) ; see LOGIC, INDUCTION, SYLLOGISM. In theology, reason, as distinguished from faith, is the human intel ligence exercised upon religious truth whether by way of discovery or by way of explanation. The limits within which the reason may be used have been laid down differently in different churches and periods of thought : on the whole, modern Christianity, espe cially in the Protestant churches, tends to allow to reason a wide field, reserving, however, as the sphere of faith the ultimate (supernatural) truths of theology.
The Greek words for reason are vows and X&yos, both vaguely used. In Aristotle the X6-yos of a thing is its definition, in cluding its formal cause, while the ultimate principles of a science are a pxat, the "reasons" (in a common modern sense) which explain all its particular facts. Noin in Plato and Aristotle is used both widely for all the meanings which "reason" can have, and strictly for the faculty which apprehends intuitively. Thus, in the Republic, vows is the faculty which apprehends necessary truth, while (34a (opinion) is concerned with phenomena.
The Schoolmen distinguished between ratio cognoscendi (a rea son for acknowledging a fact) and ratio essendi (a reason for the existence of this fact).