[6] See "Arthur Schopenhauer. Von ihm; über ihn. Ein Wort der Vertheidigung," von Ernst Otto Lindner, and "Memorabilien, Briefe und Nachlassstücke," von Julius Frauenstädt (Berlin, 1863), pp. 163-165. Upon another point, more nearly touching the real issue, I had a controversy with Schopenhauer in the year 1852. In arguing against Fichte's derivation of the _Non-Ego_ from the _Ego_ in his chief work,[7] he had said:-- [7] Schopenhauer, "Die Welt als Wille und Vorstellung," second edition, i., 37 (third edition, i., 39). "Just as if Kant had never existed, the Principle of Sufficient Reason still remains with Fichte what it was with all the Schoolmen, an _œterna veritas_: that is to say, just as the Gods of the ancients were still ruled over by eternal Destiny, so was the God of the Schoolmen still ruled over by these _œterna veritates_, _i.e._, by the metaphysical, mathematical, and metalogical truths, and even, according to some, by the validity of the moral law. These _veritates_ alone were unconditioned by anything, and God, as well as the world, existed through their necessity. Thus with Fichte the _Ego_, according to the Principle of Sufficient Reason, is the reason of the world or of the _Non-Ego_, of the Object, which is the product or result of the _Ego_ itself. He took good care, therefore, neither to examine nor to check the Principle of Sufficient Reason any farther. But if I had to indicate the particular form of this principle by which Fichte was guided in making the _Ego_ spin the _Non-Ego_ out of itself, as the spider its web, I should point to the Principle of the Sufficient Reason of Being in Space; for nothing but a reference to this principle gives any sort of sense or meaning to his laboured deductions of the way in which the _Ego_ produces and manufactures the _Non-Ego_ out of itself, which form the contents of the most senseless and--simply on this account--most tiresome book ever written. The only interest this Fichteian philosophy has for us at all--otherwise it would not be worth mentioning--lies in its being the tardy appearance of the real antithesis to ancient Materialism, which was the most consistent starting from the Object, just as Fichte's philosophy was the most consistent starting from the Subject. As Materialism overlooked the fact, that with the simplest Object it forthwith posited the Subject also; so Fichte not only overlooked the fact, that with the Subject (whatever name he might choose to give it) he had already posited the Object also, because no Subject can be thought without it; he likewise overlooked the fact, that all derivation _à priori_, nay, all demonstration whatsoever, rests upon a necessity, and that all necessity itself rests entirely and exclusively on the Principle of Sufficient Reason, because to be necessary, and to result from a given reason, are convertible terms; that the Principle of Sufficient Reason