For the effect is totally different from the cause, and
consequently can never be discovered in it. Motion in the second
billiard-ball is a quite distinct event from motion in the first;
nor is there anything in the one to suggest the smallest hint of the
other. A stone or piece of metal raised into the air, and left without
any support, immediately falls: but to consider the matter a priori,
is there anything we discover in this situation which can beget the
idea of a downward, rather than an upward, or any other motion, in the
stone or metal?
And as the first imagination or invention of a particular effect, in
all natural operations, is arbitrary, where we consult not experience;
so must we also esteem the supposed tie or connexion between the cause
and effect, which binds them together, and renders it impossible
that any other effect could result from the operation of that cause.
When I see, for instance, a billiard-ball moving in a straight line
towards another; even suppose motion in the second ball should by
accident be suggested to me, as the result of their contact or
impulse; may I not conceive, that a hundred different events might
as well follow from that cause? May not both these balls remain at
absolute rest? May not the first ball return in a straight line, or
leap off from the second in any line or direction? All these
suppositions are consistent and conceivable.
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