mere delusion of the fancy to conceive the pre-existence of the ideas,
in any chain of association, as so many differently coloured billiard-
balls in contact, so that when an object, the billiard-stick, strikes
the first or white ball, the same motion propagates itself through the
red, green, blue and black, and sets the whole in motion. No! we must
suppose the very same force, which constitutes the white ball, to
constitute the red or black; or the idea of a circle to constitute the
idea of a triangle; which is impossible.

But it may be said, that by the sensations from the objects A and M,
the nerves have acquired a disposition to the vibrations a and m, and
therefore a need only be repeated in order to re-produce m. Now we
will grant, for a moment, the possibility of such a disposition in a
material nerve, which yet seems scarcely less absurd than to say, that
a weather-cock had acquired a habit of turning to the east, from the
wind having been so long in that quarter: for if it be replied, that
we must take in the circumstance of life, what then becomes of the
mechanical philosophy? And what is the nerve, but the flint which the
wag placed in the pot as the first ingredient of his stone broth,
requiring only salt, turnips, and mutton, for the remainder! But if we
waive this, and pre-suppose the actual existence of such a
disposition; two cases are possible. Either, every idea has its own
nerve and correspondent oscillation, or this is not the case. If the
latter be the truth, we should gain nothing by these dispositions; for
then, every nerve having several dispositions, when the motion of any
other nerve is propagated into it, there will be no ground or cause
present, why exactly the oscillation m should arise, rather than any
other to which it was equally pre-disposed. But if we take the former,
and let every idea have a nerve of its own, then every nerve must be
capable of propagating its motion into many other nerves; and again,