required to test and illustrate the system by innumerable facts, to support it by the most different kinds of proof, to throw light on it from all sides, and then to place the different points of view boldly in contrast, to separate thoroughly the multifarious materials, and present them in a well-arranged whole. Therefore, although it would, no doubt, have been more agreeable to the reader to have my whole work in one piece, instead of consisting, as it now does, of two halves, which must be combined in using them, he must reflect that this would have demanded that I should accomplish at one period of life what it is only possible to accomplish in two, for I would have had to possess the qualities at one period of life that nature has divided between two quite different ones. Hence the necessity of presenting my work in two halves supplementary to each other may be compared to the necessity in consequence of which a chromatic object-glass, which cannot be made out of one piece, is produced by joining together a convex lens of flint glass and a concave lens of crown glass, the combined effect of which is what was sought. Yet, on the other hand, the reader will find some compensation for the inconvenience of using two volumes at once, in the variety and the relief which is afforded by the handling of the same subject, by the same mind, in the same spirit, but in very different years. However, it is very advisable that those who are not yet acquainted with my philosophy should first of all read the first volume without using the supplementary books, and should make use of these only on a second perusal; otherwise it would be too difficult for them to grasp the system in its connection. For it is only thus explained in the first volume, while the second is devoted to a more detailed investigation and a complete development of the individual doctrines. Even those who should not make up their minds to a second reading of the first volume had better not read the second volume till after the first, and then for itself, in the ordinary sequence of its chapters, which, at any rate, stand in some kind of connection, though a somewhat looser one, the gaps of which they will fully supply by the recollection of the first volume, if they have thoroughly comprehended it. Besides, they will find everywhere the reference to the corresponding passages of the first volume, the paragraphs of which I have numbered in the second edition for this purpose, though in the first edition they were only divided by lines.