 Another category whose relation to classes, properties, and concepts is contested is that of kinds. To judge by how we talk, kinds seem more “concrete” than properties: compare ‘I used to drive that kind of car’ versus ‘I used to drive that property’ (see Carlson  1977).  Further complicating the relationship is the fact that the notion ‘natural kind’ is the topic of a body of literature large enough to be the topic of a separate entry  (natural kinds).  This literature, which traces back at least to the discussion of “Kinds” by Mill  (1843),  is guided by a set of paradigms rather different from those that guide the literature on natural properties. For example, following Mill, it is widely denied that there is a natural kind to which all and only white things belong, on the grounds that they have nothing else important in common other than their color. So even if one identified kinds with properties, there would be a case for distinguishing the senses of ‘natural’ in ‘natural property’ and ‘natural kind’ (see Tobin  2013).  Of course this does not rule out analysing one of the notions in terms of the other: for example, being a very natural kind might require being coextensive with several different sufficiently natural properties that are probabilistically correlated given the actual laws of nature, but not necessarily equivalent (c.f. Boyd  1991).