 This suggestion has been criticized. According to Noordhof (1998: 223) it fails because it does not respect the “bulge in the carpet constraint”. For now the question which was ambiguously asked about properties, can be unambiguously asked about tropes: is it in virtue of being mental or in virtue of being physical that the trope is causally relevant for the effect (for a response, cf. Robb 2001 and Ehring 2003)? And Gibb (2004) has complained that the trope’s simple and primitive nature makes it unsuitable for membership in two such radically different classes as that of the mentally and of the physically similar tropes, respectively (for more reasons against the suggestion cf. Macdonald and Macdonald 2006).