How can know that (sensory event) A is the cause of some (sensory event) B? Since A and B are distinguishable, we do not think of one being the cause of the other until, through experience, we find constant conjunction between A and B (coupled with “contiguity” (closeness) of A and B, and the priority of A to B). This constant conjunction gives rise to a superstition that there is a necessary connection between A and B but this notion is just superstition, in that we might have had a long run of coincidences. Since A and B are separable, and we can conceive them existing apart, there is no purely rational basis for deriving B from A; and appeal to some general principle derived from experience (i. E. , the future will be like the past) is not helpful because any such principle suffers from the same problem as “A causes B” -- because this too can be coincidental.