<P> "And, moreover, we say that the former are seen, but not intellected, while the ideas are intellected but not seen ." </P> <P> Descartes often wrote of the meaning of idea as an image or representation, often but not necessarily "in the mind", which was well known in the vernacular . Despite that Descartes is usually credited with the invention of the non-Platonic use of the term, he at first followed this vernacular use . In his Meditations on First Philosophy he says, "Some of my thoughts are like images of things, and it is to these alone that the name' idea' properly belongs ." He sometimes maintained that ideas were innate and uses of the term idea diverge from the original primary scholastic use . He provides multiple non-equivalent definitions of the term, uses it to refer to as many as six distinct kinds of entities, and divides ideas inconsistently into various genetic categories . For him knowledge took the form of ideas and philosophical investigation is the deep consideration of these entities . </P> <P> In striking contrast to Plato's use of idea is that of John Locke . In his Introduction to An Essay Concerning Human Understanding, Locke defines idea as "that term which, I think, serves best to stand for whatsoever is the object of the understanding when a man thinks, I have used it to express whatever is meant by phantasm, notion, species, or whatever it is which the mind can be employed about in thinking; and I could not avoid frequently using it ." He said he regarded the book necessary to examine our own abilities and see what objects our understandings were, or were not, fitted to deal with . In his philosophy other outstanding figures followed in his footsteps--Hume and Kant in the 18th century, Arthur Schopenhauer in the 19th century, and Bertrand Russell, Ludwig Wittgenstein, and Karl Popper in the 20th century . Locke always believed in good sense--not pushing things to extremes and on taking fully into account the plain facts of the matter . He considered his common - sense ideas "good - tempered, moderate, and down - to - earth ." </P> <P> As John Locke studied humans in his work "An Essay Concerning Human Understanding" he continually referenced Descartes for ideas as he asked this fundamental question: "When we are concerned with something about which we have no certain knowledge, what rules or standards should guide how confident we allow ourselves to be that our opinions are right?" A simpler way of putting it is how do humans know ideas, and what are the different types of ideas . An idea to Locke "can simply mean some sort of brute experience ." He shows that there are "No innate principles in the mind .". Thus, he concludes that "our ideas are all experiential in nature ." An experience can either be a sensation or a reflection: "consider whether there are any innate ideas in the mind before any are brought in by the impression from sensation or reflection ." Therefore, an idea was an experience in which the human mind apprehended something . </P>

What element of thought is represented by the question what is the main idea here