Now we have already seen in what the unity to which the many states belong must be taken to consist. We found that this unity is essentially teleological; that group of states, we saw, is one thing which functions as one in regard to an end or interest, or, as we may also say, is the embodiment of coherent structure. The same is true of the process of change. The earlier and later stages of the process are differences in an identity precisely because they constitute one process. And a process is one when it is the systematic realisation of a single coherent end. To be one process means to be the systematic expression in a succession of stages of a single coherent plan or law. The succession of stages is thus welded into a unity by the singleness of the plan or law which they embody, and it is this systematic connection of each stage with all the rest which we express by saying that whatever changes possesses an underlying permanent identity of character. It would amount to precisely the same thing if we said the successive states of anything that changes form a connected system. We must be careful here, as we were in dealing with the problem of Substance, not to be misled by taking symbolic aids to imagination for philosophical truths. Just as it is easy to imagine the “substance” of things as a sort of material substratum, it is easy to imagine the identity which pervades all changes as that of a number of pieces of matter, and to think of the changes as constituted by their motion through space. But such a representation must not be taken for anything more than an aid to imagination. It helps us to make a mental diagram, but it throws absolutely no light upon the real nature of the connection between the identity and the succession. For the same problem breaks out within each of the “self-identical” pieces of matter; we have to say what we mean by calling it one and the same throughout the series of its changing positions, and the necessity of answering this question shows us at once that the identity of a material particle throughout its motion is only one _case_ of that identity pervading succession which belongs to all change, and in no sense affords any explanation of the principle it illustrates.[100] As a recent writer puts it, “it seems to be a deeply rooted infirmity of the human mind ... that it can hardly conceive activities of any sort apart from material bases, ... through habitually seeking to represent all phenomena in mechanical terms, in terms of the motion of little bits of matter, many of us have come to believe that in so doing we describe the actual events underlying phenomena.”[101] This “disease of the intellect,” as the same writer aptly calls it, is nowhere more insidious than where we are dealing with the problem of Change.