As regards this second edition, first of all I am glad to say that after five and twenty years I find nothing to retract; so that my fundamental convictions have only been confirmed, as far as concerns myself at least. The alterations in the first volume therefore, which contains the whole text of the first edition, nowhere touch what is essential. Sometimes they concern things of merely secondary importance, and more often consist of very short explanatory additions inserted here and there. Only the criticism of the Kantian philosophy has received important corrections and large additions, for these could not be put into a supplementary book, such as [pg xxiii] those which are given in the second volume, and which correspond to each of the four books that contain the exposition of my own doctrine. In the case of the latter, I have chosen this form of enlarging and improving them, because the five and twenty years that have passed since they were composed have produced so marked a change in my method of exposition and in my style, that it would not have done to combine the content of the second volume with that of the first, as both must have suffered by the fusion. I therefore give both works separately, and in the earlier exposition, even in many places where I would now express myself quite differently, I have changed nothing, because I desired to guard against spoiling the work of my earlier years through the carping criticism of age. What in this regard might need correction will correct itself in the mind of the reader with the help of the second volume. Both volumes have, in the full sense of the word, a supplementary relation to each other, so far as this rests on the fact that one age of human life is, intellectually, the supplement of another. It will therefore be found, not only that each volume contains what the other lacks, but that the merits of the one consist peculiarly in that which is wanting in the other. Thus, if the first half of my work surpasses the second in what can only be supplied by the fire of youth and the energy of first conceptions, the second will surpass the first by the ripeness and complete elaboration of the thought which can only belong to the fruit of the labour of a long life. For when I had the strength originally to grasp the fundamental thought of my system, to follow it at once into its four branches, to return from them to the unity of their origin, and then to explain the whole distinctly, I could not yet be in a position to work out all [pg xxiv] the branches of the system with the fullness, thoroughness, and elaborateness which is only reached by the meditation of many years—meditation which is 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 [pg xxv] 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.