fferent shocks and
variations and mixtures are the only changes of which matter is
susceptible, and as these never afford us any idea of thought or
perception, 'tis concluded to be impossible, that thought can ever
be caused by matter.

"Few have been able to withstand the seeming evidence of this
argument; and yet nothing in the world is more easy than to refute
it. We need only reflect upon what has been proved at large, that
we are never sensible of any connexion between causes and effects,
and that 'tis only by our experience of their constant conjunction
we can arrive at any knowledge of this relation. Now, as all
objects which are not contrary are susceptible of a constant
conjunction, and as no real objects are contrary, I have inferred
from these principles (Part III. Sec. 15) that, to consider the matter
_a priori_, anything may produce anything, and that we shall never
discover a reason why any object may or may not be the cause of any
other, however great, or however little, the resemblance may be
betwixt them. This evidently destroys the precedent reasoning,
concerning the cause of thought or perception. For though there
appear no manner of connection betwixt motion and thought, the case
is the same with all other causes and effects. Place one body of a
pound weight on one end of a lever, and another body of the same
weight on the other end; you will never find in these bodies any
principle of motion dependent on their distance from the centre,
more than of thought and perception. If you pretend, therefore, to
prove, _a priori_, that such a position of bodies can never cause
thought, because, turn it which way you will, it is nothing but a
position of bodies: you must, by the same course of reasoning,
conclude that it can never produce motion, since there is no more
apparent connection in the one than in the other. But, as this
latter conclusion is contrary to evident experience, and as 'tis
possible we may have a like experience in the operations of the
mind, and may perceive a constant conjunction of thought and
motion, you reason too hastily when, from the mere consideration of
the ideas, you conclude that 'tis impossible motion can ever
produce thought, or a different position of parts give rise to a
different passion or reflec