=The Science of Concepts.= Here the question immediately arises: how can we secure such perfection? The answer to this general preliminary question of all the sciences belongs to the sphere of the first or the most general of all the sciences, a knowledge of which is presupposed for the pursuit of the other sciences. Since its foundation by the Greek philosopher Aristotle it has borne the name of _logic_, which name, etymologically speaking, hints suspiciously at the _word_, and the word, as is known, steps in where ideas are wanting. Here, however, we have to deal with the very science of ideas, to which language bears the relation only of a means--and often an inadequate means--to an end. We have already seen how, through the physiologic fact of _memory_, experiences are found in our consciousness which are similar, that is, partially coinciding with one another. These coinciding parts are those concerning which we can make predictions, for the very reason that they coincide in every single instance, and they alone, therefore, constitute that part of our experience which bears results and hence has significance. =4. Concrete and Abstract.= Such coinciding or repeated parts of similar experiences we call, as already stated, _concepts_. But here, too, attention must immediately be drawn to a linguistic imperfection, which consists in the fact that in such a group of coinciding experiences we designate by the same name both the isolated experience or the object of a special experience and the totality of _all_ the coinciding experiences; in other words, all the similar experiences. Thus, _horse_ means, on the one hand, quite a definite thing which for the moment forms an object of our experience, and, on the other, the totality of all possible similar objects which have been present in our former experiences, and which we shall meet in our future experiences. It is true that these two sorts of contents of consciousness bearing the same name are distinguished also as _concrete_ and _abstract_, and there is an inclination to attribute "reality" only to the first, while the other, as "mere entities in thought," are relegated to a lesser degree of reality. As a matter of fact, the difference, though important, is of quite another kind. It is the difference between the _momentary experience_, as opposed to the totality of the corresponding _memories_ and _expectations_. Hence not so much a difference in _reality_ as in _presence_. However, our observations have already made it apparent that presence alone never yields knowledge. A necessary part of knowledge is the memory of former similar experiences. For without such memory and the corresponding comparison, it is quite impossible for us to get at those things which agree and which, therefore, may be predicted; and we should stand before every one of our experiences with the helplessness of a new-born babe.[A]