Mendelssohn could never take up his mind with trifles; matters of the greatest moment kept him in restless activity, such as the principles of Morals and of Natural Theology, the immortality of the soul, etc. In all these branches of inquiry, in which humanity is so deeply interested, he has also, as I hold, done as much as can be done on the principles of the Leibnitio-Wolfian philosophy. Perfection was the compass which he had constantly before his eyes, and which directed his course, in all these investigations. His God is the Ideal of the highest perfection, and the idea of the highest perfection lies at the basis of his Ethics. The principle of his Æsthetics is sensuous perfection. My discussion with him on our first acquaintance referred mainly to the following points. I was a faithful adherent of Maimonides before I became acquainted with modern philosophy; and, as such, I insisted on the negation[55] of all positive attributes to God, inasmuch as these can be represented by us only as finite. Accordingly I proposed the following dilemma: Either God is not the absolutely perfect being, in which case his attributes may by us be not only _conceived_, but also _known_, that is, represented as realities belonging to an object; or He _is_ the absolutely perfect being, and then the idea of God is conceived by us, but its reality is merely _assumed_ as problematic. Mendelssohn, on the other hand, insisted on the affirmation, with regard to God, of all realities,--a position which goes very well with the Leibnitio-Wolfian philosophy, because it requires, in order to prove the reality of an idea, nothing more than that it is thinkable, that is, fulfils the law of Non-Contradiction. My moral theory was then genuine Stoicism. It aimed at the attainment of free will and the ascendency of reason over the feelings and passions. It made the highest destination of man to be the maintenance of his _differentia specifica_, the knowledge of the truth; and all other impulses, common to us with the irrational animals, were to be put in operation merely as means to this chief end. The knowledge of the good was not distinguished by me from the knowledge of the true; for, following Maimonides, I held the knowledge of the truth to be the highest good of man. Mendelssohn, on the other hand, maintained that the idea of perfection, which lies at the basis of Ethics, is of much wider extent than the mere knowledge of the truth. All natural impulses, capacities and powers, as something good in themselves (not merely as means to something good), were to be brought into exercise as realities. The highest perfection was the idea of the maximum, or the greatest sum, of these realities.