Hume on “Causality” (continued):

Event 1: Billiard ball A hits Billiard ball B.
Event 2: Billiard ball B begins to roll away from its spot.
I assume that Event 1 is the “cause” of Event 2. But what do I actually observe?
Hume says: All you observe is that
(a)Event 1 is spatially adjacent to Event 2: they are contiguous;
(b)Event 1 is prior in time to Event 2; and
(c)Events 1 and 2 are constantly conjoined: every time you see one ball hit another, the second one moves.

Thus, you observe three things: (a) contiguity, (b) temporal priority, and (c) constant conjunction.

•When we think of Event 1 causing Event 2, however, we think of something stronger than these three: we think that there is a “necessary connection” between the events:
•We think: If ball A hits ball B, then there’s no way that B won’t move! B’s motion is inevitable, or made “necessary” by A’s impact on it.

•Hume’s challenge: Show me the “necessity”! You observe the two events, you notice their contiguity, priority and constant conjunction, but then you (illegitimately) “impose” the necessity!

•Hume’s challenge (continued): How can you be sure that the next time A hits B, B will move?
•Your reply: There is a “Law of Nature” (one of Newton’s laws of motion) that dictates that whenever A hits B, B will move. So I can predict with certainty that B will move when A hits it the next time.

•Hume’s reply to you: What is your knowledge of this “law” based on?
•You to Hume: On uniform past experience. In the past B has always moved when hit by A. What has been true in the past will continue to be true in the future.

•Hume to you: What makes you think that just because something has always happened in the past, it will continue to happen in the future? What “guarantee” is there that “the future must resemble the past”?
•You: Because in the past “the future has always resembled the past.”

•Hume: Gotcha! You’re arguing in a circle! You are relying on the assumption that the future will resemble the past in order to support the assumption that the future will resemble the past. That’s “begging the question!”