repeated, will leave a trace, or miniature, of themselves, as one vibration, which will recur every now and then, from slight causes. Much rather, therefore, may the part b of the compound miniature a + b recur, when the part A of the compound original vibration A + B is impressed.
And as the ninth proposition may be thus made to prove the present, so it ought to be acknowledged and remarked here, that unless the ninth be allowed, the present cannot be proved, or that the power of association is founded upon, and necessarily requires, the previous power of forming ideas, and miniature vibrations. For ideas, and miniature vibrations, must first be generated, according to the eighth and ninth propositions, before they can be associated, according to the tenth and this eleventh. But then (which is very remarkable) this power of forming ideas, and their corresponding miniature vibrations, does equally presuppose the power of association. For since all sensations and vibrations are infinitely divisible, in respect of time and place, they could not leave any traces or images of themselves, i.e. any ideas, or miniature vibrations, unless their infinitesimal parts did cohere together through joint impression, i.e. association. Thus, to mention a gross instance, we could have no proper idea of a horse, unless the particular ideas of the head, neck, body, legs, and tail, peculiar to this animal, stuck to each other in the fancy, from frequent joint impression. And, therefore, in dreams, where complex associations are much weakened, and various parcels of visible ideas, not joined in nature, start up together in the fancy, contiguous to each other, we often see monsters, chimeras, and combinations, which have never been actually presented.
Association seems also necessary to dispose the medullary substance to this or that miniature vibration, in succession, after the miniatures of a large number of original vibrations have been generated.
Nor does there seem to be any precise limit which can be set to this mutual dependence of the powers of generating miniatures, and of association upon each other: however they may both take place together, as the heart and brain are supposed to do, or both depend upon one simple principle; for it seems impossible, that they should imply one another ad infinitum. There is no greater difficulty here than in many other cases of mutual indefinite implication, known and allowed by all. Nay, one may almost deduce some presumption in favour of the hypothesis here produced, from this mutual indefinite implication of its parts so agreeable to the tenor of nature in other things. And it is certainly a presumption in its favour, that a less power of generating miniatures will be a foundation for a larger of association, and vice versâ, till, at last, the whole superstructure of ideas and associations observable in human life may, by proceeding upwards according to analysis, and downwards according
