Hume claims that matters of fact are falsely founded on the relation of cause and effect. He describes the relationship of cause and effect as "a principle of connection between different thoughts or ideas," introducing one another with regularity. For instance, if a man were to find a watch on a desert island, he would automatically assume that the island had once been inhibited. Hume argues that we have no foundation on which to "reduce the principles productive of natural phenomena to a greater simplicity and to resolve the many particular effects into a few general causes." (H,639) .
Hume's argument is that, to the best of our knowledge, every known effect is independent of any known cause. We cannot be certain that there exists a cause and effect relationship because we are incapable of proving its existence by pure reason. Our basis for arguing the existence of this relationship is solely dependent on custom and resemblance. Hume supports this claim with an example concerning the nourishment of bread. He discusses how when eating bread, we assume that it will, and must provide us with some form of nourishment. However, Hume argues that this claim is based on the "foundation that the future will resemble the past and that similar powers will be conjoined with similar sensible qualities." (H,642) He argues that we have no reason to know for certain that eating bread will, in turn nourish us. We only believe it will because it has not failed to do so in the past. Hume claims that there is no argument that can prove this resemblance of the past and future. Therefore, what is known as causal connection is merely a constant conjunction. .
Hume provides yet another reason supporting the claim that nothing in the world is connected necessarily with anything else. He argues that it is not logically impossible to "suppose those conjunctions not to hold that, as a matter of fact, do hold." (Warnock,60) For instance, one can imagine that while cooling a bucket of water to zero degrees Celsius, it will burst into flames at that exact temperature instead of freezing.
