From a hundred possible confutations let one suffice. According to this system the idea or vibration a from the external object A becomes associable with the idea or vibration m from the external object M, because the oscillation a propagated itself so as to re-produce the oscillation m. But the original impression from M was essentially different from the impression A: unless therefore different causes may produce the same effect, the vibration a could never produce the vibration m: and this therefore could never be the means, by which a and m are associated. To understand this, the attentive reader need only be reminded, that the ideas are themselves, in Hartley’s system, nothing more than their appropriate configurative vibrations. It is a 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, there is no reason assignable, why the vibration m should arise, rather than any other ad libitum.