Hume goes on to examine and attack the occasionalist picture, which suggests that what we perceive as "causes" are in fact "occasions" and that God is the ultimate cause of all change. Considering the limitations of the human intellect, Hume ponders what stroke of logic could possibly produce such unsupported and outlandish conclusions. Further, he questions how we might know the forces that are operated by the mind of God if we cannot even decipher the forces that are operated by our own minds and bodies.
The motivation behind Hume's brief discussion of probability might not be readily apparent. Considering his emphasis on the scientific method, we should not be surprised that Hume carries a deterministic worldview: nothing that happens happens purely by chance. We may not be able to predict the outcomes of dice rolls, but this is simply because we cannot adequately calculate all the relevant factors. Hume will address the difficult question of how free will might be reconciled with this determinism in section VIII.
Hume's determinism should suggest to us that his skepticism is epistemological and not metaphysical. That is, Hume does not believe that it is pure coincidence that billiard ball collisions always happen in the same way. Rather, he believes that we are incapable of rationalizing the causal connection. We might read Hume as saying that everything that happens happens according to some sort of law or necessity, but that these laws or necessities are beyond our understanding.
We invent the notion of probability and chance, Hume suggests, because we cannot actually determine precisely how things will happen. These probabilities are determined by experience. For instance, if car crashes kill passengers 80 percent of the time, I will judge it highly probable that a car crash will result in death. Other probabilities are 100 percent certain: for instance, flames always burn. This certainty does not then result from observing directly some power of causation or necessary connection, but comes instead from a calculation of probability based on experience. Hume's discussion of probability explains his tendency to see reasoning about matters of fact as determined by habit and experience rather than by an understanding of causation.
A little more straightforward in its intent and methodology, section VII returns to the central line of Hume's argument in the Enquiry. This section is meant to establish what precisely we mean when we talk about causation.
Before we continue, perhaps we should clear up the distinction between causation and necessary connection. Generally speaking, we can say that A causes B if B temporally succeeds A, if A and B are spatially contiguous, and if B always follows A. However, if I always hum while striking a match, we can hardly say that my humming causes the match to burst into flame, even though it satisfies all the above criteria. Causation must also rely on some kind of necessary connection: the match could still burst into flame if I didn't hum, but it couldn't burst into flame if I didn't strike it. The question for Hume, then, is how we can know or perceive this necessary connection. What is it about the striking of the match and not my humming that connects to the match's bursting into flame?