 The Kripke–Putnam arguments for essentialism are, in effect, direct appeals to intuition. For Ellis and Lowe, the dialectical basis for essentialism is that essentialism is a core part of what they each take to be the optimal metaphysical system. Ellis (2001, 145–50) regards his essentialist metaphysics as supported by his argument that it yields a stronger argument for scientific realism. In particular, for Ellis the essences of natural kinds explain the laws of nature: laws are grounded in the world’s natural kind structure, which includes not only natural kinds of thing but also natural kinds of process and event. Above it was mentioned that for Lowe (2006, 144) laws concern natural kinds; by contrast, for Ellis laws are grounded in essential facts about kinds. As a consequence, the laws of nature are metaphysically necessary. This has the advantage of explaining what natural necessity is (it is just metaphysical necessity), but at the cost of denying the intuitive contingency of laws. Lowe, on the other hand, holds that laws can be grounded in the contingent possession of properties by kinds, and so need not be metaphysically necessary.