Since, as has been said, this whole work is only the unfolding of a single thought, it follows that all its parts have the most intimate connection with each other. Not merely that each part stands in a necessary relation to what immediately precedes it, and only presupposes a recollection of that by the reader, as is the case with all philosophies which consist merely of a series of inferences, but that every part of the whole work is related to every other part and presupposes it. It is, therefore, necessary that the reader should remember not only what has just been said, but all the earlier parts of the work, so that he may be able to connect them with what he is reading, however much may have intervened. Plato also makes this demand upon his readers through the intricate digressions of his dialogues, in which he only returns to the leading thought after long episodes, which illustrate and explain it. In our case this demand is necessary; for the breaking up of our one single thought into its many aspects is indeed the only means of imparting it, though not essential to the thought itself, but merely an artificial form. The division of four principal points of view into four books, and the most careful bringing together of all that is related and homogeneous, assists the exposition and its comprehension; yet the material absolutely does not admit of an advance in a straight line, such as the progress of history, but necessitates a more complicated exposition. This again makes a repeated study of the book necessary, for thus alone does the connection of all the parts with each other become distinct, and only then do they all mutually throw light upon each other and become quite clear.(68)