other causes are wanting, almost in the same manner as in a concert of music the air is agitated by vibrations of a very complex kind. But then, as in a concert, some one instrument generally strikes the ear more than the rest, so of the complex vibrations which exist in the medullary substance, some one part will prevail over the rest, and present the corresponding idea to the mind. Some region must be disposed, at each instant, to vibrate stronger than the rest; and of the specific vibrations which are generally impressed upon this region, some one will have a more favourable concurrence of circumstances than the rest. And thus it will follow, according to the terms of the proposition, that sensory vibrations, by being sufficiently repeated, will beget a disposition to miniature vibrations corresponding to them respectively; or, using the appellations above assumed, that A, B, C, &c. will beget a, b, c, &c.
If we allow the proof of this proposition thus deduced from the nature of vibratory motions, and of an animal body, the foregoing proposition will follow from it, and hold equally, in respect of the senses of feeling, taste, and smell, as of sight and hearing. Or, in other words, if we allow that original impressed vibratory motions leave a tendency to miniature ones of the same kind, place, and line of direction, it will follow, that sensations must beget ideas, and that not only in the senses of sight and hearing, where the ideas are sufficiently vivid and distinct, but in the three others, since their sensations are also conveyed to the mind by means of vibratory motions. We may also perhaps discover hereafter, from the nature of vibratory motions, and of the human brain, compared with the circumstances of life, why the ideas of one sense are more vivid and distinct than those of another.
Sensations may be said to be associated together, when their impressions are either made precisely at the same instant of time, or in the contiguous successive instants. We may therefore distinguish association into two sorts, the synchronous, and the successive.
The influence of association over our ideas, opinions, and affections, is so great and obvious, as scarcely to have escaped the notice of any writer who has treated of these, though the word association, in the particular sense here affixed to it, was first brought into use by Mr. Locke. But all that has been delivered by the ancients and moderns, concerning the power of habit, custom, example, education, authority, party-prejudice, the
