 Mendelssohn employs the expression “right of nature” (Naturrecht) to designate the sum of the laws of natural right resulting from the application of these rational principles to individual cases. Given this one universal law of nature, the concepts of moral philosophy are sufficiently connected with one another to make up a theoretical system and it is possible to develop “all our duties, rights, and obligations” from that natural law. The result is a moral philosophy as certain as metaphysics, namely, a “science of the qualities [Beschaffenheiten] of an entity with free will.” At the same time, he contends that the derivation, not only of the universal natural law, but also of various maxims from it (“Love virtue,” “control your passions”) is as certain as any geometric proof. Yet, unlike geometry, ethics is about human action and this science is, moreover, “erected on the grounds of metaphysics,” in particular, the metaphysical doctrines of God, the world, and the human soul. Hence, evidence in moral philosophy is necessarily even more difficult to obtain than in metaphysics. While the foundational principles of ethics can be proven with the same certainty (Gewissheit) as those of geometry, it is not on the same level with respect to its ability to be comprehended (Fasslichkeit). Unlike geometry, ethics supposes the comprehension of those metaphysical truths.