The division between natural kinds – the kinds that ‘cut nature at its joints’ – and those that simply reflect human interests and values has a long history. The natural kinds are often thought to have certain essential characteristics that are fixed by nature, such as a particular atomic number, while other kinds, of which a commonly cited example is race, are contentious precisely because they appear to group things, in this case people, by features that reflect social mores and not real essences. That natural versus socially constructed difference, of course, depends on what an essence is as well as whether having an essence is the mark of a natural kind. In Natural Categories and Human Kinds: Classification in the Natural and Social Sciences (Cambridge University Press, 2013), Muhammad Ali Khalidi, associate professor of philosophy at York University, argues for what he calls an “epistemic” view of natural kinds, in which they are the kinds that correspond to our best scientific categories and satisfy various epistemic virtues. On his view, natural kinds do not have essences, often have fuzzy boundaries, can satisfy the relevant epistemic virtues to differing degrees, and can be mind-dependent in a way that does not impugn their objectivity. The result is a challenging view of natural kinds that avoids problems associated with essentialist views, but also widens the scope of what may be a natural kind to include potentially many of those often considered to be socially-constructed.