In order to see clearly what an idea is, we must guard ourselves against a misunderstanding. Many regard the idea as the form or the differentiation of our thinking, and according to this opinion we have the idea in our mind, in so far as we are thinking of it, and each separate time that we think of it anew we have another idea although similar to the preceding one. Some, however, take the idea as the immediate object of thought, or as a permanent form which remains even when we are no longer contemplating it. As a matter of fact our soul has the power of representing to itself any form or nature whatsoever when the occasion arises for thinking about it, and I think that this power of our soul, so far as it expresses some nature, form or essence, is properly the idea of the thing. This is in us, and is always in us, whether we are thinking of it or no. For our soul expresses God and the universe and all essences as well as all existences. This position is in accord with my principles, for there is no natural means by which anything can enter our minds from the outside, and it is a bad habit we have of thinking as if our minds received certain “forms” as messengers from the outer world, or as if they had doors or windows. We have in our minds all those forms for all periods of time because the mind at every moment expresses all its future thoughts and already thinks confusedly of all that of which it will ever think distinctly. Nothing can be taught us of which we have not the idea already in our minds. The idea is as it were the material out of which the thought will form itself. This is what Plato has excellently brought out in his doctrine of reminiscence, a doctrine which contains a great deal of truth, provided that it is properly understood and purged of the error of preexistence, and provided that one does not conceive of the soul as having already known and thought distinctly at some other time what it learns and thinks now. Plato has also confirmed his position by a beautiful argument. He introduces a small boy whom he leads by short steps to extremely difficult truths of geometry bearing on incommensurables, all this without teaching the boy anything, merely drawing out replies by a well-arranged series of questions. This shows that the soul virtually knows those things, and needs only to be reminded in order to recognize those truths, and consequently that it possesses at least the ideas upon which those truths depend. We may say even that it already possesses those truths, if we consider them as the relations of the ideas.