 Kant thought Hume’s argument led to an unacceptable, skeptical conclusion, and he rejected Hume’s own solution to the skepticism (see Kant’s Critique of Pure Reason, B5, B19–20). Hume suggested that our idea of causal necessity is grounded merely in custom or habit, since it is generated by our own imaginations after repeated observations of one sort of event following another sort of event (see Hume’s A Treatise of Human Nature, Book I, Section VI; Hegel also rejected Hume’s solution, see EL §39). For Kant, science and knowledge should be grounded in reason, and he proposed a solution that aimed to reestablish the connection between reason and knowledge that was broken by Hume’s skeptical argument. Kant’s solution involved proposing a Copernican revolution in philosophy (Critique of Pure Reason, Bxvi). Nicholas Copernicus was the Polish astronomer who said that the earth revolves around the sun, rather than the other way around. Kant proposed a similar solution to Hume’s skepticism. Naïve science assumes that our knowledge revolves around what the world is like, but, Hume’s criticism argued, this view entails that we cannot then have knowledge of scientific causes through reason. We can reestablish a connection between reason and knowledge, however, Kant suggested, if we say—not that knowledge revolves around what the world is like—but that knowledge revolves around what we are like. For the purposes of our knowledge, Kant said, we do not revolve around the world—the world revolves around us. Because we are rational creatures, we share a cognitive structure with one another that regularizes our experiences of the world. This intersubjectively shared structure of rationality—and not the world itself—grounds our knowledge.