 Another important exegetical issue that arises in the Essay is whether Locke thought that there are natural kinds based on real essences. Scientific disciplines categorize the objects they study into kinds. To say that a kind is natural is to say that a grouping of similar individuals exists independently of human decisions. The hope of each scientific discipline is to identify as many natural kinds as possible within their domain and to determine their properties accurately. To this end, we create scientific taxonomies, like the periodic table of elements, the phylogenetic tree, etc., to organize the kinds we have identified and to study their properties. On the face of it, the question of whether there are natural kinds in Locke seems to be the same as the question of whether there are species, and as we saw above (in §§1–3) Locke denies that there are natural species. However, it is possible to distinguish between a species (a classification humans make based on observed similarities) and a natural kind (a grouping that occurs naturally and independently of human naming practices). Locke is clearly aware of this distinction, so it is possible that what he has said about sorting and nominal essences only reveals what he thinks about nominal essences and our practice of sorting, which is a semantic issue, not about the metaphysics of nature.