 There is, then, considerable disagreement about how to interpret the notion of neutrality. The notion of monism raises its own problems. But since these are questions faced by all forms of monism, they are, perhaps, not quite as pressing as the problems surrounding neutrality. Much like one can distinguish different versions of neutral monism on the basis of the notion of neutrality that they employ, it is possible to distinguish different versions of the doctrine, based on the various ways in which the notion of monism is understood (see Schaffer 2016). Neutral monism might, for example, be interpreted as a form of existence monism—the view that only a single concrete thing exists; but it might also interpreted as a monism about the kinds of things there are—the view that concrete things, be they simple or complex, are of the same neutral kind. The evidence suggests that all past and present versions of neutral monism have been pluralist on both these counts: they work with a plurality of entities, most particularly, with a plurality of basic neutral entities; and, given their focus on the mind-body problem, they recognize at least mental and physical kinds of entities in addition to the neutral entities. All entities belonging to such non-neutral kinds must, however, count as derivative. In the final analysis, all entities must be basic neutral entities or complexes of basic neutral entities.