 In the Essay, Locke develops this idea of the rational deduction of natural law somewhat further, setting it in the context of a more mature and coherent theory of ideas than we find in the Essays on the Law of Nature. In the Essay, moral ideas assume a particular significance owing to their place in Locke’s general taxonomy of ideas. For Locke, all the basic contents of the mind are simple ideas. These are formed by the mind into what Locke terms complex ideas, which are combinations of simple ideas made in the pattern of our perceptions of things in the extra mental world, or according to a pattern created by reason alone. Moral ideas fall into the second category of complex idea, falling under the technical heading complex ideas of modes. Modes are a specific kind of complex ideas, created by the mind from simple ideas of sensation or reflection, but referring to no extra-mental reality. They are not intended as natural kinds, but are products of the mind alone, referring to purely conceptual archetypes. They are best understood in contradistinction to ideas of substances, which are created by the mind but aim to mirror the real essences of extra-mental things—for example, the idea cat is intended to capture a kind of thing in the world that has a specific set of perceivable characteristics. Ideas of substances fail in mirroring reality, however, as they can never be complete representations of the world outside the mind. Modal ideas, on the other hand, are a special kind of idea for Locke, and actually hold out the promise for real knowledge. Modal ideas are ideas by which we fully grasp the real essence of things, because the mind, in some sense, is the originator of them (I will return to this in the next paragraph). The idea of a triangle is a modal idea, made by reason and knowable in its essence with complete accuracy. The idea of a triangle is a product of the mind, and does not refer to anything outside the mind—i.e., any external archetype. The kinds of ideas that fall into this category are the idea of God, mathematical concepts, and, most importantly for our present purposes, moral concepts. Locke writes, 