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Idea. In the Platonic philosophy the idea or eidos is the eternal and unchangeable archetype to which all the objects forming a class conform. The world of sense is in a state of perpetual flux - ever coming into existence and ceasing to be - it is the sphere of the non-existent, and material objects are reeel only in so far as they partake of the nature of their eidos. The ideal world extends wherever there is anything capable of becoming an object of thought; there are ideas of beauty, justice, and truth, as well as of a man, a house, or a tree. All the other ideas culminate in the Idea of the One, the Divine Being which is the source of all other being. When the word "idea" was used in this sense, Idealism and Realism were identical, and the mediceval schoolmen who supported the Platonic view were rightly called "Realists." [Nominalist.] But with the growth of modern philosophy "idea" assumed a totally different meaning. It was now used by Locke, as previously by Descartes, to denote any presentation or representation in the mind - ' whatever is the (immediate) object of the mind in thinking"; while Hume confined it to representations in the mind produced by memory or association, as opposed to impressions which are the direct result of sense-perception. The idea thus came to be regarded as a peculiar property of the mind, and, when schools arose which denied the existence of a material world, they were called ' idealists," the notion being that they reduced all existence into "ideas," mental products independent of any agency save that of some mind. On the other hand, those who maintained that the external world has an independent objective existence became known as "realists."

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