Capitalism as we know it presents typical dialectical features that isolate it from nature, in which real oppositions make evolution revolutionary: A dialectical metaphysics replaces the free flow of events allowing capitalist relationships but preventing the practice of materialism. Some radically sceptical issues in Hume's Enquiry Concerning Human Understanding, Dialogues Concerning Natural Religion and A Treatise of Human Nature come useful here. A materialistic approach with complete (i.e., non-dialectical) ruptures in fact dovetails with Hume's argument on the unpredictability of nature and the predictability of human social activities. As a consequence, a thus renewed materialistic political economy concerned with the concrete must work out its own categories dynamically, to discard them once they have been proved metaphysical.