The Sun Will Rise Tomorrow
An infamous objection to this reasoning is David Hume’s argument in “Sceptical Doubts Concerning the Operations of the Understanding.”² He divides all knowledge into Matters of Fact and Relations of Ideas. The negation of the former would not be a contradiction, while the negation of latter would be a contradiction. Another feature of each of these is that Matters of Fact rely on observation to be true, while Relations of Ideas rely on deductive reasoning. Hume points out that our understanding holds ideas about the unobserved, such as that the sun will rise
tomorrow. That the sun does not rise tomorrow is not a contradiction, so it is not a Relation of Ideas. Moreover, it is not yet observed, so it isn’t a Matter of Fact. Since these types of ideas do not seem to fit in either classification, it is necessary to see how we reach them. Hume points out that we know that every A observed so far has been accompanied by a B, so we conclude from that that the next A will be accompanied by a B. The missing premise here is to say that every A is accompanied by a B. But that would be circular, as the conclusion we are trying to make is already captured in that premise. In other words, to say that every A is accompanied by a B would depend on the event that the next A will be accompanied by a B, and that would be circular.
