Humes skepticism

Reason supports the relation between ideas but matters of fact need to depend on the connection of cause and effect that we get through the experience. A priori reasoning can not hold up the causes of effects but Hume postulates a necessary connection that is depended on the uniformity of nature. In terms of ideas, these regularities appear in the form of Spatio-temporal sequences. Thus, by the law of association, the presence of one of these ideas (or their corresponding impression) raises the idea of the other in the mind.

On the other hand, these matters of fact do not offer the degree of necessity of the formal sciences at all and "are not ascertained in the same way since the opposite of any matter of fact is still possible because it never implies a contradiction". Hume discusses that because we cannot perceive this necessary connection connecting events, the question of whether or not they really exist is irrelevant and futile.