  One worry about this proposal is that it appears to raise the Exclusion Problem all over again, this time at the level of properties (tropes). If a single property is both mental and physical, Completeness and No Overdetermination force us to say that it’s efficacious only qua physical, not qua mental. (For this and other criticisms, see Noordhof 1998; Raymont 2001; Gibb 2004; Macdonald and Macdonald 2006; Alward 2008; Maurin 2008; see Robb 2013 for some replies.)