 Hume thinks it is evident that demonstrative reasoning can’t bridge the gap between (1) and (2). However unlikely it may be, we can always intelligibly conceive of a change in the course of nature. Even though aspirin relieved my previous headaches, there’s no contradiction in supposing that it won’t relieve the one I’m having now, so the supposition of a change in the course of nature can’t be proven false by any reasoning concerning relations of ideas.