 Finally, D.M. Armstrong (1979) has stated a regress argument similar to Bradley’s, as a threat to class nominalists. The thought is that since class nominalists analyze particulars’ having of properties in terms of particulars’ membership in a class of things that all have those properties, they would incur a regress when trying to define a membership relation. However, class nominalists like Lewis (2002), have been adamant about not being committed to a membership relation of any sort; indeed, Lewis has argued that all we have is a “singular-to-plural copula: ‘is one of’ as in ‘this is one of those’.” (Lewis 2002: 10, italics mine).