 The weak form of the thesis that metaphysics is impossible is this: there is something about the human mind (perhaps even the minds of all rational agents or all finite rational agents) that unfits it for reaching metaphysical conclusions in any reliable way. This idea is at least as old as Kant, but a version of it that is much more modest than Kant's (and much easier to understand) has been carefully presented in McGinn 1993. McGinn's argument for the conclusion that the human mind is (as a matter of evolutionary contingency, and not simply because it is “a mind”) incapable of a satisfactory treatment of a large range of philosophical questions (a range that includes all metaphysical questions), however, depends on speculative factual theses about human cognitive capacities that are in principle subject to empirical refutation and which are at present without significant empirical support. For a different defense of the weak thesis, see Thomasson 2009.