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.