IDEA, This word has borne very distinct meanings in the history of philosophy. Down to the 17th c., it had the signification given to it by Plato, and referred to the Platonic doctrine of eternal forms existing in the Divine mind, according to which the world and all sensible things were framed. Plato made a grand distinction between the intelligible, or what occupied the intellect, and the senatble; the one represented the eternal, the immutable, and the certain; the other, the mutable and fleeting part of the universe. The forms preceded the matter; the actual circles occurring in nature were produced from a pre-existing ideal circle holding a place in the Divine intelligence; the actual men were generated from an ideal man. The word was used in this sense in lit erature as well as in philosophy clown to the 17th c., as in Spenser, Shakespeare, Hooker, and Milton. Thus in Paradise Lost Sir W. Hamilton dates the change that came over the application of the word from the publication of Descartes's Discourse on Method in 1637, remarking, however, that in a treatise by David Buchanan, published at Paris the year before, the new meaning had been introduced. " The fortune of this word is curious. Employed by Plato to express the real forms of the intelligible world, in lofty contrast to the unreal images of the sen sible, it was lowered by Descartes, who extended it to the objects of our consciousness in general. When, after Gassendi, the school of Condillac had analyzed our highest faculties into our lowest, the idea was still more deeply degraded from its high original. Like a fallen angel, it was relegated from the sphere of Divine intelligence to the atmos phere of human sense; till at last ideologie (more correctly idealogie), a word which could only properly suggest an ez priori scheme, deducing our knowledge from the intellect, has in France become the name peculiarly distinctive of that philosophy of mind which exclusively derives our knowledge from the senses."—Hamilton's Discussions, p. 70.
In speaking of the mental representation of external things, Descartes, instead of employing the various terms image, species, phantasm, etc., which had been the words formerly in use for that particular. signification, used the word idea. In this be was
followed by other philosophers, as, for example, Locke, who states that he has adopted the word to stand for " whatever is the object of the understanding, when a man thinks." Thus the mental impression that we are supposed to have when thinking of the sun without seeing the actual object. is called our idea of the sun. The idea is thus in con trast with the sensation, or the feeling that we have when the senses arc engaged directly or immediately upon the thing itself. The sensation is what constitutes the thing, the reality: the impression persisting after the thing has gone, and recoverable by mental causes without the original, is the idea. Although the word in this application may lie so guarded as to lead to no bad consequences, Dr, Reid was of opinion that it gave coun tenance to the setting up of a new and fictitious element in the operations of the mind. This, however, raises the great question of metaphysics—namely, the exact nature of our knowledge of an external world. See PERCEPTION.
It is difficult to avoid the use of the word idea, and yet, owing to the looseness of its application, there is a danger of its not conveying a definite signification. We need a general word to express the contrast to sensation, or to actuality; and no better term has yet been found than idea, being what is common to memory and to imagination, and expressing the mind as not under the present impression of real objects, but as, by its own tenacity and associating powers, having those objects to all practical ends before its view. Thus, all our sensations, whether of sight, hearing, touch, taste, or smell, and all the feelings that we have in the exercise of our moving energies, become transformed into ideas when, without the real presence of the original agency, we can deal with them in the way of pursuit or avoidance, or can discriminate and compare them, nearly as if in their first condition as sensation. Sir W. Hamilton, in his Lectures on Logic 12% has endeavored to avoid employing the word, but other writers on mental philosophy have freely adopted it in the above acceptation. See also GENERALIZATION and IMAGI NATION.