 One concern with anti-realist accounts has to do with the source of classification of determinates under a determinable term or concept. As above, this is usually taken to involve inexact resemblance, but if inexact resemblance is primitive, then objections of the sort leveled against resemblance nominalist treatments of inexact resemblance may arise, mutatis mutandis (see Fales [1990: 117–20] for discussion, and Rodriguez-Pereyra [2002] for a recent response). An alternative means of classification of determinates appeals to “naturalness” (as per Lewis 1983) as a primitive property binding determinates into classes, but this approach incurs ontological commitment and, it might be complained, is not clearly explanatory. Perhaps the most developed approach to determinate classification is Armstrong’s, on which “the resemblance of determinate universals is constituted by partial identity, where the greater the resemblance the greater degree of identity” (1997: 51), such that, for example, determinate lengths resemble in virtue of sharing unit length  universals.[24]  Armstrong argues that his account makes sense of various features of determination: Determinate opponent incompatibility is accommodated since, e.g., an object’s length cannot be identical to different sums of unit lengths; Determinate similarity/comparability is accommodated since different determinate lengths share some but not all unit lengths; Asymmetric dependence is accommodated since specific sums of unit lengths entail the having of length, but not vice versa. It has been complained, however, that his account cannot handle the full range of  cases.[25] 