This “variable realization” argument has led many philosophers to seek an alternative way of reconciling the efficacy of mental and other special causes with the causal closure thesis, one which does not require the strict identity of non-physical and physical properties. The general idea of this “non-reductive physicalism” is to allow that instantiations of a given special property will always be grounded in or metaphysically determined by instantiations of physical properties, but to add that these “realizing” physical properties might be different in different cases. So, for example, any being who thinks about the square root of two will do so in virtue of instantiating some physical properties, but these can be different physical properties in different cases—in one human being it may be one set of neural arrangements, in another a different set, and in other life forms it might involve nothing like neural properties at all.