This faculty of ideal abstraction furnishes the _conditio sine quâ non_ to all grades in the development of thought; for by it alone can we compare idea with idea, and thus reach ever onwards to higher and higher levels, as well as to more and more complex structures of ideation. As to the history of this development we shall have more to say presently. Meanwhile I desire only to remark two things in connection with it. The first is that throughout this history the development is a _development_: the faculty of abstraction is everywhere the same in _kind_. And the next thing is that this development is everywhere dependent on the faculty of _language_. A great deal will require to be said on both these points in subsequent chapters; but it is needful to state the facts thus early—and they are facts which psychologists of all schools now accept,—in order to render intelligible the next step which I am about to make in my classification of ideas. This step is to distinguish between the faculty of abstraction where it is not dependent upon language, and where it is so dependent. I have just said that the faculty of abstraction is _everywhere_ the same in kind; but, as I immediately proceeded to affirm that the _development_ of abstraction is dependent upon language, I have thus far left the question open whether or not there can be any rudimentary abstraction without language. It is to this question, therefore, that we must next address ourselves. On the one hand it may be argued that by restricting the term abstract to ideas which can only be formed by the aid of language, we are drawing an arbitrary line—fixing upon one degree in the continuous scale of a faculty which is throughout the same in kind. For, say some psychologists, it is evident that in our own case most of our more simple abstract or general ideas are not dependent for their existence upon words. Or, if this be disputed, these psychologists are able to point to infants, and even to the lower animals, in proof of their assertion. For an infant undoubtedly exhibits the possession of simple general ideas prior to the possession of any articulate language; and after it begins to use such language it does so by spontaneously widening the generality of signification attaching to its original words. In proof of both these statements numberless observations might be quoted, and further on will be quoted; but here I need only wait to give one in proof of each. As regards the first, Professor Preyer tells us that at eight months old,[17] and therefore long before it was able to speak, his child was able to classify all glass bottles as resembling—or belonging to the order of—a feeding-bottle.[18] As regards the second, M. Taine tells us of a little girl eighteen months old, who was amused by her mother hiding in play behind a piece of furniture, and saying “Coucou.” Again, when her food was too hot, when she went too near the fire or candle, and when the sun was warm,