# Observations on Man (6th edition)/Part I/Chapter III/Section IV
### Section IVSection IV

OF MEMORY.
Memory was defined in the introduction to be that faculty by which traces of sensations and ideas recur, or are recalled, in the same order and proportion, accurately or nearly, as they were once presented.
Now here we may observe,
First, That memory depends entirely or chiefly on the state of the brain. For diseases, concussions of the brain, spirituous liquors, and some poisons, impair or destroy it; and it generally returns again with the return of health, from the use of proper medicines and methods. And all this is peculiarly suitable to the notion of vibrations. If sensations and ideas arise from peculiar vibrations, and dispositions to vibrate, in the medullary substance of the brain, it is easy to conceive, that the causes above alleged may so confound the sensations and ideas, as that the usual order and proportion of the idea shall be destroyed.
Secondly, The rudiments of memory are laid in the perpetual recurrency of the same impressions, and clusters of impressions. How these leave traces, in which the order is preserved, may be understood from the eighth, ninth, tenth, and eleventh propositions.
The traces which letters, and words, i.e. clusters of letters, leave, afford an instance and example of this. And, as in languages the letters are fewer than the syllables, the syllables than the words, and the words than the sentences, so the single sensible impressions, and the small clusters of them, are comparatively few in respect of the large clusters; and, being so, they must recur more frequently, so as the sooner to beget those traces which I call the rudiments or elements of memory. When these traces or ideas begin to recur frequently, this also ​contributes to fix them, and their order, in the memory, in the same manner as the frequent impression of the objects themselves.
Thirdly, Suppose now a person so far advanced in life, as that he has learnt all these rudiments, i.e. that he has ideas of the common appearances and occurrences of life, under a considerable variety of subordinate circumstances, which recur to his imagination from the slightest causes, and with the most perfect facility; and let us ask, how he can be able to remember or recollect a past fact, consisting of one thousand single particulars, or of one hundred such clusters as are called the rudiments of memory; ten single particulars being supposed to constitute a rudiment? First, then, We may observe, that there are only one hundred links wanting in the chain; for he has already learnt considerable exactness in the subordinate circumstances of the one hundred clusters; and perfect exactness is not to be supposed or required.—Secondly, The one hundred clusters recur again and again to the imagination for some time after the fact, in a quick and transient manner, as those who attend sufficiently to what passes in their own minds may perceive; and this both makes the impression a little deeper, and also serves to preserve the order. If the person attempts to recollect soon after the impression, the effect remaining in the brain is sufficient to enable him to do this with the accuracy required and experienced; if a longer time intervene, before he attempts to recollect, still the number of involuntary recurrences makes up in some measure for the want of this voluntary recollection. However, the power of recollection declines in general, and is entirely lost by degrees. It confirms this reasoning, that a new set of strong impressions destroys this power of recollection. For this must both obliterate the effects of the foregoing impressions, and prevent the recurrency of the ideas.—Thirdly, As the single impressions, which make the small clusters, are not combined together at hazard, but according to a general tenor in nature, so the clusters which make facts succeed each other according to some general tenor likewise. Now this both lessens the number of varieties, and shews that the association between many of the clusters, or rudiments, or one hundred links supposed to be wanting, is cemented already. This may be both illustrated and exemplified by the observation, that it is difficult to remember even well-known words that have no connexion with each other, and more so to remember collections of barbarous terms; whereas adepts in any science remember the things of that science with a surprising exactness and facility.—Fourthly, Some clusters are excluded from succeeding others, by ideas of inconsistency, impossibility, and by the methods of reasoning, of which we become masters as we advance in life.—Fifthly, The visible impressions which concur in the past fact, by being vivid, and preserving the order of place, often contribute greatly to preserve the order of time, and to suggest the clusters which may be ​wanting.—Sixthly, It is to be observed, that as we think in words, both the impressions and the recurrences of ideas will be attended with words; and these words, from the great use and familiarity of language, will fix themselves strongly in the fancy, and by so doing bring up the associated trains of ideas in the proper order, accurately or nearly. And thus, when a person relates a past fact, the ideas do in some cases suggest the words, whilst in others the words suggest the ideas. Hence illiterate persons do not remember nearly so well as others, cæteris paribus. And I suppose the same is true of deaf persons in a still greater degree. But it arises hence also, that many mistakes in the subordinate circumstances are committed in the relations of past facts, if the relater descend to minute particulars. For the same reasons these mistakes will be so associated with the true facts after a few relations, that the relater himself shall believe that he remembers them distinctly.—Seventhly, The mistakes which are committed both on the foregoing account and others, make considerable abatements in the difficulty here to be solved.
Fourthly, Let it now be asked, in what the recollection of a past fact, consisting of one hundred clusters, as above, differs from the transit of the same one hundred clusters, over the fancy, in the way of a reverie? I answer, partly in the vividness of the clusters, partly and principally in the readiness and strength of the associations, by which they are cemented together. This follows from what has been already delivered; but it may be confirmed also by many other observations.—Thus, first, Many persons are known by relating the same false story over and over again, i.e. by magnifying the ideas, and their associations, at last to believe that they remember it. It makes as vivid an impression upon them, and hangs as closely together, as an assemblage of past facts recollected by memory.—Secondly, All men are sometimes at a loss to know whether clusters of ideas that strike the fancy strongly, and succeed each other readily and immediately, be recollections, or mere reveries. And the more they agitate the matter in the mind, the more does the reverie appear like a recollection. It resembles this, that if in endeavouring to recollect a verse, a wrong word, suiting the place, first occurs, and afterwards the right one, it is difficult during the then present agitation to distinguish the right one. But afterwards, when this agitation is subsided, the right word easily regains its place. Persons of irritable nervous systems are more subject to such fallacies than others. And madmen often impose upon themselves in this way, viz. from the vividness of their ideas and associations, produced by bodily causes. The same thing often happens in dreams. The vividness of the new scene often makes it appear like one that we remember, and are well acquainted with.—Thirdly, If the specific nature of memory consist in the great vigour of the ideas, and their associations, ​then, as this vigour abates, it ought to suggest to us a length of time elapsed; and vice versâ, if it be kept up, the distance of time ought to appear contracted. Now this last is the case: for the death of a friend, or any interesting event, often recollected and related, appears to have happened but yesterday, as we term it, viz. on account of the vividness of the clusters, and their associations, corresponding to the nature of a recent event.—Fourthly, It is not, however, to be here supposed, that we have not many other ways of distinguishing real recollections from mere reveries. For the first are supported by their connexion with known and allowed facts, by various methods of reasoning, and having been related as real recollections, &c.
Fifthly, In like manner we distinguish a new place, book, person, &c. from one which we remember, supposing both to be presented in like circumstances. The parts, associates, &c. of that which we remember, strike us more strongly, are suggested by each other, and hang together, which does not hold of the new. The old does also suggest many associates, which a new one in like circumstances would not. And if from the then state of fancy, the distance of time, &c. there be any doubt of these things either with respect to the old or new, a like doubt arises in respect of the memory. An attentive person may observe, that he determines of such things, whether they be old or new, by the vividness of the ideas, and their power of suggesting each other, and foreign associates.
Some persons seem to suppose, that the soul surveys one object, the old for instance, and comparing it with the impressions which a similar new one would excite, calls the old one an object remembered. But this is like supposing an eye within the eye to view the pictures made by objects upon the retina. Not to mention, that the soul cannot in the same instant, during the same τό νυν survey both the old and new, and compare them together; nor is there any evidence, that this is done in fact. A person who inquires into the nature of memory, may indeed endeavour to state the difference between the impressions of old and new, as I have done here; but this is a speculation that few persons concern themselves with, whereas all remember and apply the words relative to memory just as they do other words. We may conclude therefore, that the difference of vividness and connexion in the ideas, with the other associates of recollections, are a sufficient foundation for the proper use of the words relative to the memory, just as in other like cases.
Sixthly, The peculiar imperfection of the memory in children tallies with the foregoing account of this faculty; and indeed this account may be considered as a gross general history of the successive growth of the memory, in passing from childhood to adult age. Children must learn by degrees the ideas of single impressions, the clusters which I call rudiments, and the most usual connexions and combinations of these. They have also ​the use of words, and of objects and incidents, as signs and symbols, with the proper method of reasoning upon them, to learn; and during their noviciate in these things their memories must labour under great imperfections. It appears also, that the imperfections peculiar to children correspond in kind as well as degree to the reasons here assigned for them. Their not being able to digest past facts in order of time is, in great measure, owing to their not having the proper use of the symbols, whereby time is denoted.
Seventhly, The peculiar imperfection of the memory in aged persons tallies also with the foregoing account. The vibrations, and dispositions to vibrate, in the small medullary particles, and their associations, are all so fixed by the callosity of the medullary substance, and by repeated impressions and recurrences, that new impressions can scarce enter, that they recur seldom, and that the parts which do recur bring in old trains from established associations, instead of continuing those which were lately impressed. Hence one may almost predict what very old persons will say or do upon common occurrences. Which is also the case frequently with persons of strong passions, for reasons that are not very unlike. When old persons relate the incidents of their youth with great precision, it is rather owing to the memory of many preceding memories, recollections, and relations, than to the memory of the thing itself.
Eighthly, In recovering from concussions, and other disorders of the brain, it is usual for the patient to recover the power of remembering the then present common incidents for minutes, hours, and days, by degrees; also the power of recalling the events of his life preceding his illness. At length he recovers this last power perfectly, and at the same time forgets almost all that passed in his illness, even those things which he remembered, at first, for a day or two. Now the reason of this I take to be, that upon a perfect recovery the brain recovers its natural state, i.e. all its former dispositions to vibrate; but that such as took place during the preternatural state of the brain, i.e. during his illness, are all obliterated by the return of the natural state. In like manner dreams, which happen in a peculiar state of the brain, i.e. in sleep, vanish, as soon as vigilance, a different state, takes place. But if they be recollected immediately upon waking, and thus connected with the state of vigilance, they may be remembered. But I shall have occasion to be more explicit on this head in the next Section.
Ninthly, It is very difficult to make any plausible conjectures why some persons of very weak judgments, not much below idiots, are endued with a peculiar extraordinary memory. This memory is generally the power of recollecting a large group of words, suppose, as those of a sermon, in a short time after they are heard, with wonderful exactness and readiness; but then the whole is obliterated, after a longer time, much more completely ​than in persons of common memories and judgments. One may perhaps conjecture, that the brain receives all dispositions to vibrate sooner in these persons, and lets them go sooner, than in others. And the last may contribute to the first: for, new impressions may take place more deeply and precisely, if there be few old ones to oppose them. The most perfect memory is that which can both receive most readily, and retain most durably. But we may suppose, that there are limits, beyond which these two different powers cannot consist with each other.
Tenthly, When a person desires to recollect a thing that has escaped him, suppose the name of a person, or visible object, he recalls the visible idea, or some other associate, again and again, by a voluntary power, the desire generally magnifying all the ideas and associations; and thus bringing in the association and idea wanted, at last. However, if the desire be great, it changes the state of the brain, and has an opposite effect; so that the desired idea does not recur, till all has subsided; perhaps not even then.
Eleventhly, All our voluntary powers are of the nature of memory; as may be easily seen from the foregoing account of it, compared with the account of the voluntary powers given in the first chapter. And it agrees remarkably with this, that, in morbid affections of the memory, the voluntary actions suffer a like change and imperfection.
Twelfthly, For the same reasons the whole powers of the soul may be referred to the memory, when taken in a large sense. Hence, though some persons may have strong memories with weak judgments, yet no man can have a strong judgment with a weak original power of retaining and remembering.