The second demand is this, that the introduction be read before the book itself, although it is not contained in the book, but appeared five years earlier under the title, “Ueber die vierfache Wurzel des Satzes vom zureichenden Grunde: eine philosophische Abhandlung” (On the fourfold root of the principle of sufficient reason: a philosophical essay). Without an acquaintance with this introduction and propadeutic it is absolutely impossible to understand the present work properly, and the content of that essay will always be presupposed in this work just as if it were given with it. Besides, even if it had not preceded this book by several years, it would not properly have been placed before it as an introduction, but would have been incorporated in the first book. As it is, the first book does not contain what was said in the earlier essay, and it therefore exhibits a certain incompleteness on account of these deficiencies, which must always be supplied by reference to it. However, my disinclination was so great either to quote myself or laboriously to state again in other words what I had already said once in an adequate manner, that I preferred this course, notwithstanding the fact that I might now be able to give the content of that essay a somewhat better expression, chiefly by freeing it from several conceptions which resulted from the excessive influence which the Kantian philosophy had over me at the time, such as—categories, outer and inner sense, and the like. But even there these conceptions only occur because as yet I had never really entered deeply into them, therefore only by the way and quite out of connection with the principal matter. The correction of such passages in that essay will consequently take place of its own accord in the mind of the reader through his acquaintance with the present work. But only if we have fully recognised by means of that essay what the principle of sufficient reason is and signifies, what its validity extends to, and what it does not extend to, and that that principle is not before all things, and the whole world merely in consequence of it, and in conformity to it, a corollary, as it were, of it; but rather that it is merely the form in which the object, of whatever kind it may be, which is always conditioned by the subject, is invariably known so far as the subject is a knowing individual: only then will it be possible to enter into the method of philosophy which is here attempted for the first time, and which is completely different from all previous methods.
But the same disinclination to repeat myself word for word, or to say the same thing a second time in other and worse words, after I have deprived myself of the better, has occasioned another defect in the first book of this work. For I have omitted all that is said in the first chapter of my essay “On Sight and Colour,” which would otherwise have found its place here, word for word. Therefore the knowledge of this short, earlier work is also presupposed.
Finally, the third demand I have to make on the reader might indeed be tacitly assumed, for it is nothing but an acquaintance with the most important phenomenon that has appeared in philosophy for two thousand years, and that lies so near us: I mean the principal writings of Kant. It seems to me, in fact, as indeed has already been said by others, that the effect these writings produce in the mind to which they truly speak is very like that of the operation for cataract on a blind man: and if we wish to pursue the simile further, the aim of my own work may be described by saying that I have sought to put into the hands of those upon whom that operation has been successfully performed a pair of spectacles suitable to eyes that have recovered their sight—spectacles of whose use that operation is the absolutely necessary condition. Starting then, as I do to a large extent, from what has been accomplished by the great Kant, I have yet been enabled, just on account of my earnest study of his writings, to discover important errors in them. These I have been obliged to separate from the rest and prove to be false, in order that I might be able to presuppose and apply what is true and excellent in his doctrine, pure and freed from error. But not to interrupt and complicate my own exposition by a constant polemic against Kant, I have relegated this to a special appendix. It follows then, from what has been said, that my work presupposes a knowledge of this appendix just as much as it presupposes a knowledge of the philosophy of Kant; and in this respect it would therefore be advisable to read the appendix first, all the more as its content is specially related to the first book of the present work. On the other hand, it could not be avoided, from the nature of the case, that here and there the appendix also should refer to the text of the work; and the only result of this is, that the appendix, as well as the principal part of the work, must be read twice.
The philosophy of Kant, then, is the only philosophy with which a thorough acquaintance is directly presupposed in what we have to say here. But if, besides this, the reader has lingered in the school of the divine Plato, he will be so much the better prepared to hear me, and susceptible to what I say. And if, indeed, in addition to this he is a partaker of the benefit conferred by the Vedas, the access to which, opened to us through the Upanishads, is in my eyes the greatest advantage which this still young century enjoys over previous ones, because I believe that the influence of the Sanscrit literature will penetrate not less deeply than did the revival of Greek literature in the fifteenth century: if, I say, the reader has also already received and assimilated the sacred, primitive Indian wisdom, then is he best of all prepared to hear what I have to say to him. My work will not speak to him, as to many others, in a strange and even hostile tongue; for, if it does not sound too vain, I might express the opinion that each one of the individual and disconnected aphorisms which make up the Upanishads may be deduced as a consequence from the thought I am going to impart, though the converse, that my thought is to be found in the Upanishads, is by no means the case.
But most readers have already grown angry with impatience, and burst into reproaches with difficulty kept back so long. How can I venture to present a book to the public under conditions and demands the first two of which are presumptuous and altogether immodest, and this at a time when there is such a general wealth of special ideas, that in Germany alone they are made common property through the press, in three thousand valuable, original, and absolutely indispensable works every year, besides innumerable periodicals, and even daily papers; at a time when especially there is not the least deficiency of entirely original and profound philosophers, but in Germany alone there are more of them alive at the same time, than several centuries could formerly boast of in succession to each other? How is one ever to come to the end, asks the indignant reader, if one must set to work upon a book in such a fashion?
As I have absolutely nothing to advance against these reproaches, I only hope for some small thanks from such readers for having warned them in time, so that they may not lose an hour over a book which it would be useless to read without complying with the demands that have been made, and which should therefore be left alone, particularly as apart from this we might wager a great deal that it can say nothing to them, but rather that it will always be only pancorum hominum, and must therefore quietly and modestly wait for the few whose unusual mode of thought may find it enjoyable. For apart from the difficulties and the effort which it requires from the reader, what cultured man of this age, whose knowledge has almost reached the august point at which the paradoxical and the false are all one