the following reflections may, perhaps, suffice. Were any object
presented to us, and were we required to pronounce concerning the
effect, which will result from it, without consulting past observation;
after what manner, I beseech you, must the mind proceed in this
operation? It must invent or imagine some event, which it ascribes to
the object as its effect; and it is plain that this invention must be
entirely arbitrary. The mind can never possibly find the effect in the
supposed cause, by the most accurate scrutiny and examination. 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. Why
then should we give the preference to one, which is no more consistent
or conceivable than the rest? All our reasonings _a priori_ will never