to synthesis, be built upon as small a foundation as we please. Thus we may observe, that neither does this eleventh proposition necessarily require the ninth, in its full extent, not vice versâ, for their demonstration. The least miniatures, with the feeblest cohesions of their parts, will, by degrees, run into larger, with stronger cohesions, from the same principles; nor are there any visible limits to the influence and extent of these powers, supposing the natural faculties of the being under consideration sufficiently extended.
Let me add, that the generation of sensible ideas from sensations, and the power of raising them from association, when considered as faculties of the mind, are evident and unquestionable. Since therefore sensations are conveyed to the mind, by the efficiency of corporeal causes of the medullary substance, as is acknowledged by all physiologists and physicians, it seems to me, that the powers of generating ideas, and raising them by association, must also arise from corporeal causes, and consequently admit of an explication from the subtle influences of the small parts of matter upon each other, as soon as these are sufficiently understood; which is farther evinced from the manifest influences of material causes upon our ideas and associations, taken notice of under the second proposition. And as a vibratory motion is more suitable to the nature of sensation than any other species of motion, so does it seem also more suitable to the powers of generating ideas, and raising them by association. However, these powers are evident independently, as just now observed; so that the doctrine of association may be laid down as a certain foundation, and a clew to direct our future inquiries, whatever becomes of that of vibrations.
In order to explain and prove this proposition, it will be requisite to give some previous account of the manner in which simple ideas of sensation may be associated together.
Case 1. Let the sensation A be often associated with each of the sensations B, C, D, &c. i.e. at certain times with B, at certain other times with C, &c. it is evident, from the tenth proposition, that A, impressed alone, will, at last, raise b, c, d, &c. all together, i.e. associate them with one another, provided they belong to different regions of the medullary substance; for if any two, or more, belong to the same region, since they cannot exist together in their distinct forms, A will raise something intermediate between them.
Case 2. If the sensations A, B, C, D, &c. be associated together, according to various combinations of twos, or even threes, fours, &c. then will A raise b, c, d, &c. also B raise a, c, d, &c. as in case the first.
