Occam's razor
This argument was criticized by Peter Glassen in a debate with J. J. C. Smart in the pages of "Philosophy" in the late 1970s and early 1980s. Glassen argued that, because it is not a physical entity, Occam's razor cannot consistently be appealed to by a physicalist or materialist as a justification of mental states or events, such as the belief that dualism is false. The idea is that Occam's razor may not be as "unrestricted" as it is normally described (applying to all qualitative postulates, even abstract ones) but instead concrete (only applies to physical objects). If one applies Occam's Razor unrestrictedly, then it recommends monism until pluralism either receives more support or is disproved. If one applies Occam's Razor only concretely, then it may not be used on abstract concepts (this route, however, has serious consequences for selecting between hypotheses "about" the abstract).