idea in the seventeenth and eighteenth centuries, whatever is immediately before the mind when one thinks. The notion of thinking was taken in a very broad sense; it included perception, memory, and imagination, in addition to thinking narrowly construed. In connection with perception, ideas were often (though not always – Berkeley is the exception) held to be representational images, i.e., images of something. In other contexts, ideas were taken to be concepts, such as the concept of a horse or of an infinite quantity, though concepts of these sorts certainly do not appear to be images. An innate idea was either a concept or a general truth, such as ‘Equals added to equals yield equals’, that was allegedly not learned but was in some sense always in the mind. Sometimes, as in Descartes, innate ideas were taken to be cognitive capacities rather than concepts or general truths, but these capacities, too, were held to be inborn. An adventitious idea, either an image or a concept, was an idea accompanied by a judgment concerning the non-mental cause of that idea. So, a visual image was an adventitious idea provided one judged of that idea that it was caused by something outside one’s mind, presumably by the object being seen. See also BERKELEY , DESCARTES , HUME , LOCKE , PERCEPTIO. G.S.P.