10. This explanation of the Platonic ideas, though not positively false, is exceedingly misleading. It is not positively false, because ideas are in truth the truth, the light of all science. But it is exceedingly misleading, because it conveys the impression that they are not equally essential to our simplest acts of thought and knowledge, and that there may be a lower species of knowledge into which ideas do not enter. The truth, however, is, that ideas are just as essential to our ordinary and most familiar cognitions, as they are to our most recondite and elaborate sciences, and it is in their relation to common thinking that they ought to be studied much more than in their relation to scientific cognition. We shall perceive their necessity, we shall understand them as part and parcel of ourselves, much more clearly when we view them as conditions without which no thought or knowledge of any kind is possible, than we should do if we viewed them merely as certain requisites which contributed to the construction of science. Plato speaks of them, as I have said, very frequently under the latter relation. But there is sufficient evidence that he regarded them under the former as well, under that relation which I venture to think is much the more important of the two. Leaving his expositors, then, to interpret the ideas as essential to the constitution of science, I shall explain them principally, if not exclusively, as necessary to the existence of our simplest knowledge, and as that without which no thinking of any kind could take place.
