ARTHUR SCHOPENHAUER. FRANKFURT AM MAIN, _September, 1847._ EDITOR'S PREFACE TO THE THIRD EDITION. In the present volume I lay before the public the Third Edition of the "Fourfold Root," including the emendations and additions left by Schopenhauer in his own interleaved copy. I have already had occasion elsewhere to relate that he left copies of all his works thus interleaved, and that he was wont to jot down on these fly-leaves any corrections and additions he might intend inserting in future editions. Schopenhauer himself prepared for the press all that has been added in the present edition, for he has indicated, by signs in the original context corresponding to other similar signs in the MS. passages, the places where he wished his additions to be inserted. All that was left for me to do, was to give in extended form a few citations he had purposed adding. No essential corrections and additions, such as might modify the fundamental thoughts of the work, will be found in this new edition, which simply contains corrections, amplifications, and corroborations, many of them interesting and important. Let me take only a single instance: § 21, on the "Intellectual Nature of Empirical Perception." As Schopenhauer attached great importance to his proof of the _intellectual nature_ of perception, nay, believed he had made a new discovery by it, he also worked out with special predilection all that tended to support, confirm, and strengthen it. Thus we find him in this § 21 quoting an interesting fact he had himself observed in 1815; then the instances of Caspar Hauser and others (taken from Franz's book, "The Eye," &c. &c.); and again the case of Joseph Kleinhaus, the blind sculptor; and finally, the physiological confirmations he has found in Flourens' "De la vie et de l'intelligence des Animaux." An observation, too, concerning the value of Arithmetic for the comprehension of physical processes, which is inserted into this same paragraph, will be found very remarkable, and may be particularly recommended to those who are inclined to set too high a value on calculation. Many interesting and important additions will be found in the other paragraphs also. One thing I could have wished to see left out of this Third Edition: his effusions against the "professors of philosophy." In a conversation with Schopenhauer in the year 1847, when he told me how he intended to "chastise the professors of philosophy,"[6] I expressed my dissent on this point; for even in the Second Edition these passages had interrupted the measured progress of objective inquiry. At that time, however, he was not to be persuaded to strike them out; so they were left to be again included in this Third Edition, where the reader will accordingly once more find them, although times have changed since then.