As for (2), some philosophers reject the requirement that if properties are the only ultimate constituents of reality, then they must be capable of existing in isolation from all other wholly distinct properties (Simons 1994; Denkel 1997). Properties can be both the only ultimate constituents of reality and inter-dependent. This response requires the rejection of the Humean principle that the basic independent units of being can exist in any combination, including unaccompanied (Schaffer 2003, 126). A very different response to (2) rejects the necessity of trope clustering altogether (Williams 1966, 97; Campbell 1981, 479; Schaffer 2003).