A model often used to convey the action-causes-action view is that of a pool table. The motion of one pool ball, leading to a collision with a second ball, is said to "cause" the latter's motion. As Peikoff points out (

), however, if the first entity had been an egg or a soap bubble instead of a hard ball, then its motion, assuming the same velocity as before, would not have been followed by the same result. (For an illustration, click each of the three entities in the demonstration below.) Even with hard balls, the result is highly dependent on the masses of both balls. In fact, a major reason why this model fools people is that we expect all pool balls to have the same, uniform mass. The motions on the pool table can be fully and successfully explained only by reference to the attributes of the pool balls themselves, that is, the entities causing the action.

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