57. On the whole it may appear to the reader, that the simple ideas of sensation must run into clusters and combinations, by association ; and that each of these mill, at last, coalesce into one compound or complex idea. It appears also from observation, that many of our mental or intellectual ideas (that is, those in which no particular idea of sensation is perceptible) such as those which belong to the heads of beauty, honour, moral qualities, &c. are, in fact, thus composed of parts, which by degrees coalesce into one complex idea. And as this coalescence of simple into complex ideas is thus evinced, both by the theory of association and by observation, so it may be illustrated and further con firmed, by the similar coalescence of let ters into syllables and words, in which as sociation is likewise a chief instrument.
58. If the number of simple ideas which compose the complex idea he very great, it may happen that the complex ideas shall not appear to bear any relation to its corn. ponent parts, nor to the external senses by which the original sensations were receiv ed. The reason of this is, that each sin. gle idea is overpowered by the sum of all the rest, as soon as they are all intimately united together. Thus in very compound medicines, the several tastes and flavours of the separate ingredients are lost and overpowered by the complex one of the whole mass : so that this has a taste and flavour of its own, which appears to be simple and original. Thus also white ap pears, and is vulgarly thought to be, the simplest of all colours, while.yet it really arises from a certain mixture of the seven primary colours in their due shades and proportions. And to resume the illustra tion above-mentioned, to one unacquaint ed with the arts of readingand writing, it could not appear probable, that the great variety of complex sounds in language are to be analysed into a few simple sounds. One may hope, therefore, that by pursu ing and perfecting the doctrine of associa tion, we may some time or other be ena bled to analyse all that vast variety of complex ideas which pass under the names of ideas of reflection, abstract ideas, de sires, affections, &c. into their simple com ponent parts, that is, into the simple ideas of sensation of which they are formed. This would be greatly analogous to the representation of complex articulate sounds by alphabetical signs, and to the revolution of colours, or of natural bodies, into their simple constituent parts. The complex ideas here spoken of are gene rally excited by words or visible objects ; but they are also connected with other external impressions, and depend upon them as symbols. In whatever way we
consider them, the trains of them which are presented to the mind seem to depend upon the then present state of the body, the external impressions and the remain ing influence of prior impressions and as sociations taken together.
59 As simple ideas of sensation run in to complex ones by association, so com plex ideas run into decomplex ones by association. But here the varieties of the associations, which increase with the com plexity, hinder particular ones from being so close and permanent between the com plex parts of decomplex ideas, as between the simple parts of complex ones.
60 The simple ideas of sensation arc not all equally and uniformly concerned in forming complex and decomplex ideas, but, on the contrary, some occur much oftener than others ; and the same holds good of complex ideas as the component parts of decomplex ideas : and innumer able combinations never occur at all in real life, and eonsequeutly are never asso ciated into complex and decomplex ideas. Just as in languages, some letters, and combinations of letters, occur much more frequently than others, and some combi nations never occur at all.—Further, as persons who speak the same language have, however, a different use and extent of words, so, though mankind in all ages and nations agree, in general, in their complex and decomplex ideas, yet there are many particular differences in them, and these differences are greater or less, according to the difference or resemblance in age, constitution, education, profession, country, period, &c. that is, in their im pressions and associations.
61. When sensations and ideas, with their most common combinations, have been often presented to the mind, a train of them, of considerable length, may, by once occurring, produce such a tendency to recurrence, that they may recur, with. out the previous cause, in nearly the same order and proportion as in this single oc currence. For since each of the particu lar sensations and ideas is familiar, little more will be wanting for their recurrency than a few connecting links : and even these may, in some instances, be supplied by former similar instances. These con siderations, when duly unfolded, seem to explain the chief phenomena of memory ; and it will be easily seen from them, that the memory of adults, and of proficients in any science, ought to be much more ready and certain than that of children and novices, as it is found to be in fact.