This exploration serves to clarify the distinction between matters of fact and relations of ideas and indicates their important implications.

             Hume comes up with the relation of cause and effect as the only way to reason beyond our senses. Hume then decides that the only way that we come to think in terms of cause and effect is through experience, defeating the validity of the second argument of the principle of induction. We can never know the effect of anything unless we have experienced it. This applies to objects as well as events. We are unaware of the effects of gunpowder, magnates, or food until we experience them because there is nothing in the qualities that we sense in any of these that indicates what they will potentially do. The same goes for events, such as the collision of billiard balls. There is nothing in the motion of the billiard balls indicating that they will communicate motion to each other unless we have seen it happen before (133).

             The only certainty that we have is relations of ideas but they do not actually tell us anything to explain ultimate causation. Breaking down all thought into two categories has shown that we can never reason about anything in the world such as if the sun will rise, because our only forms of reasoning tell us nothing for certain. This is a very important part of Hume's "sceptical doubts" about induction from past experience to future expectations. He argues that reasoning is not the basis for making conclusions from the experience of cause and effect. He qualifies this argument by reminding us that we will assume certain causes to have certain effects even though we do not understand the reasons why they behave that way. We do not know the true connection between the sensible qualities of the cause and the sensible qualities of the effect, we simply infer one from the other because of past experience (135). We jump from a premise that we can be sure of, that an object has always had a certain effect, to the premise that all objects with similar properties will have similar effects.