  By themselves, these observations pose no special problem for the  philosopher of mind. While the notion of a causally relevant property calls for analysis (Horgan 1989; Dardis 1993; Braun 1995), there is no reason at the outset for a token-identity theorist to be  especially concerned about the efficacy of mental properties. Gus smiles because of the way his food tastes, that phenomenal  property; Lilian walks to school along a particular route because of  what she believes, that representational property. Assuming the  mind is something physical, why should a mind’s causing behavior in virtue of its mental properties be any more puzzling than a  paperweight’s causing a square impression in virtue of its shape?