176. The connection of ideas by a sign seems necessary. The most universal and most convenient of these signs is language; but we must not forget that it is an arbitrary sign, as is proved by the variety of words used in different languages to express the same idea. 177. The phenomenon of the relation of ideas to language originates in the necessity of perpetuating ideas by determinate signs; and the importance of speech results from its being the most general, most convenient, and most flexible sign. And hence it is that when these circumstances can be united in another sign, the same object is attained. Physically speaking, written language is very different from language spoken; nevertheless, in very many cases it answers equally well. 178. The internal language is, sometimes, rather a reflection in which the idea is enlarged and developed, than an expression of it. True, we do not ordinarily think without speaking inwardly; but as we have already observed, speech is an arbitrary sign, and consequently we cannot establish a perfectly exact parallel between ideas and the internal language. 179. We think with instantaneousness, which defies the succession of words, however rapid we may suppose them to be. It is true that the internal language is far more rapid than the external; but it always involves succession, and requires a greater or less time, according to the words to be spoken. This observation is important, lest we too greatly exaggerate the relation of ideas to speech. Language is certainly a wonderful channel for the communication of ideas, and a powerful auxiliary of our understanding; but we can, without ignoring these qualities, take care to avoid that exaggeration which seems to pronounce all thought impossible, if some word thought does not correspond to it.