…the bizarreness of metaphysics is this: Common sense is incoherent in matters of metaphysics. Detailed examination of the consequences of our commonsense opinions inevitably leads to contradictions. To develop a coherent metaphysics in detail thus necessarily involves rejecting some aspects of common sense. Although ordinary common sense serves us fairly well in negotiating our everyday social and physical environments, it has not proven a reliable guide in cosmology or microphysics or neuroscience or evolutionary biology or probability theory or structural engineering or medicine or macroeconomics or topology. If metaphysics more closely resembles items in the second class than in the first, as it seems to, we might justifiably be suspicious of the dependability of common sense as a guide to metaphysics. Undependability does not imply incoherence, but it does seem a natural next step in this particular case, especially since it would generate a tidy explanation of the historical fact that detailed metaphysical systems are never thoroughly commonsensical.