# Observations on Man (6th edition)/Part I/Chapter III/Section V
### Section VSection V

OF IMAGINATION, REVERIES, AND DREAMS.
The recurrence of ideas, especially visible and audible ones, in a vivid manner, but without any regard to the order observed in past facts, is ascribed to the power of imagination or fancy. Now here we may observe, that every succeeding thought is the result either of some new impression, or of an association with the preceding. And this is the common opinion. It is impossible indeed to attend so minutely to the succession of our ideas, as to ​distinguish and remember for a sufficient time the very impression or association which gave birth to each thought; but we can do this as far as it can be expected to be done, and in so great a variety of instances, that our argument for the prevalence of the foregoing principle of association in all instances, except those of new impressions, may be esteemed a complete induction.
A reverie differs from imagination only in that the person being more attentive to his own thoughts, and less disturbed by foreign objects, more of his ideas are deducible from association, and fewer from new impressions.
It is to be observed, however, that in all the cases of imagination and reverie, the thoughts depend, in part, upon the then state of body or mind. A pleasurable or painful state of the stomach or brain, joy or grief, will make all the thoughts warp their own way, little or much. But this exception is as agreeable to the foregoing theory, as the general prevalence of association just laid down.
We come next to dreams. I say then, that dreams are nothing but the imaginations, fancies, or reveries of a sleeping man; and that they are deducible from the three following causes; viz. First, The impressions and ideas lately received, and particularly those of the preceding day. Secondly, The state of the body, particularly of the stomach and brain. And, thirdly, Association.
That dreams are, in part, deducible from the impression and ideas of the preceding day, appears from the frequent recurrence of these in greater or lesser clusters, and especially of the visible ones, in our dreams. We sometimes take in ideas of longer date, in part, on account of their recency: however, in general, ideas that have not affected the mind for some days, recur in dreams only from the second or third cause here assigned.
That the state of the body affects our dreams, is evident from the dreams of sick persons, and of those who labour under indigestions, spasms, and flatulencies.
Lastly, We may perceive ourselves to be carried on from one thing to another in our dreams partly by association.
It is also highly agreeable to the foregoing theory to expect, that each of the three foregoing causes should have an influence upon the trains of ideas that are presented in dreams.
Let us now see how we can solve the most usual phænomena of dreams upon these principles.
First, then, The scenes which present themselves are taken to be real. We do not consider them as the work of the fancy; but suppose ourselves present, and actually seeing and hearing what passes. Now this happens, First, Because we have no other reality to oppose to the ideas which offer themselves, whereas in the common fictions of the fancy, while we are awake, there is always a set of real external objects striking some of our senses, and precluding a like mistake there: or, if we become quite inattentive to external objects, the reverie does so far put ​on the nature of a dream, as to appear a reality. Secondly, The trains of visible ideas, which occur in dreams, are far more vivid than common visible ideas; and therefore may the more easily be taken for actual impressions. For what reasons these ideas should be so much more vivid, I cannot presume to say. I guess, that the exclusion of real impressions has some share, and the increased heat of the brain may have some likewise. The fact is most observable in the first approaches of sleep; all the visible ideas beginning then to be more than usually glaring.
Secondly, There is a great wildness and inconsistency in our dreams. For the brain, during sleep, is in a state so different from that in which the usual associations were formed, that they can by no means take place as they do during vigilance. On the contrary, the state of the body suggests such ideas, amongst those that have been lately impressed, as are most suitable to the various kinds and degrees of pleasant and painful vibrations excited in the stomach, brain, or some other part. Thus a person who has taken opium, sees either gay scenes, or ghastly ones, according as the opium excites pleasant or painful vibrations in the stomach. Hence it will follow, that ideas will rise successively in dreams, which have no such connexion as takes place in nature, in actual impressions, nor any such as is deducible from association. And yet, if they rise up quick and vividly one after another, as subjects, predicates, and other associates use to do, they will be affirmed of each other, and appear to hang together. Thus the same person appears in two places at the same time; two persons appearing successively in the same place coalesce into one; a brute is supposed to speak (when the idea of voice comes from that quarter), or to handle; any idea, qualification, office, &c. coinciding in the instant of time with the idea of one’s self, or of another person, adheres immediately, &c. &c.
Thirdly, We do not take notice of, or are offended at, these inconsistencies; but pass on from one to another. For the associations, which should lead us thus to take notice, and be offended, are, as it were, asleep; the bodily causes also hurrying us on to new and new trains successively. But if the bodily state be such as favours ideas of anxiety and perplexity, then the inconsistency and apparent impossibility, occurring in dreams, are apt to give great disturbance and uneasiness. It is to be observed likewise, that we forget the several parts of our dreams very fast in passing from one to another; and that this lessens the apparent inconsistencies, and their influences.
Fourthly, It is common in dreams for persons to appear to themselves to be transferred from one place to another, by a kind of sailing or flying motion. This arises from the change of the apparent magnitude and position of the images excited in the brain, this change being such as a change of distance and position in ourselves would have occasioned. Whatever the reasons be, ​for which visible images are excited in sleep, like to the objects with which we converse when awake, the same reasons will hold for changes of apparent magnitude and position also; and these changes in fixed objects, being constantly associated with motions in ourselves when awake, will infer these motions when asleep. But then we cannot have the idea of the vis inertiæ of our own bodies, answering to the impressions in walking; because the nerves of the muscles either do not admit of such miniature vibrations in sleep; or do not transmit ideas to the mind in consequence thereof; whence we appear to sail, fly, or ride. Yet sometimes a person seems to walk, and even to strike, just as in other cases he seems to feel the impression of a foreign body on his skin.
Those who walk and talk in their sleep, have evidently the nerves of the muscles concerned so free, as that vibrations can descend from the internal parts of the brain, the peculiar residence of ideas, into them. At the same time the brain itself is so oppressed, that they have scarce any memory. Persons who read inattentively, i.e. see and speak almost without remembering, also those who labour under such a morbid loss of memory, as that though they see, hear, speak, and act, pro re nata, from moment to moment, yet they forget all immediately, somewhat resemble the persons who walk and talk in sleep.
Fifthly, Dreams consist chiefly of visible imagery. This agrees remarkably with the perpetual impressions made upon the optic nerves and corresponding parts of the brain during vigilance, and with the distinctness and vividness of the images impressed.
We may observe also, that the visible imagery in dreams is composed, in a considerable degree, of fragments of visible appearances lately impressed. For the disposition to these vibrations must be greater than to others, cæteris paribus, at the same time that by the imperfection and interruption of the associations, only fragments, not whole images, will generally appear. The fragments are so small, and so intermixed with other fragments and appearances, that it is difficult to trace them up to the preceding day; the shortness of our memory contributing also not a little thereto.
It happens in dreams, that the same fictitious places are presented again and again at the distance of weeks and months, perhaps during the whole course of life. These places are, I suppose, compounded at first, probably early in youth, of fragments of real places, which we have seen. They afterwards recur in dreams, because the same state of brain recurs; and when this has happened for some successions, they may be expected to recur at intervals during life. But they may also admit of variations, especially before frequent recurrency has established and fixed them.
Sixthly, It has been observed already, that many of the things which are presented in dreams, appear to be remembered by us, ​or, at least, as familiar to us; and that this may be solved by the readiness with which they start up, and succeed one another, in the fancy.
Seventhly, It has also been remarked, that dreams ought to be soon forgotten, as they are in fact; because the state of the brain suffers great changes in passing from sleep to vigilance. The wildness and inconsistency of our dreams render them still more liable to be forgotten. It is said that a man may remember his dreams best by continuing in the same posture in which he dreamt; which, if true, would be a remarkable confirmation of the doctrine of vibrations; since those which take place in the medullary substance of the brain would be least disturbed and obliterated by this means.
Eighthly, the dreams which are presented in the first part of the night are, for the most part, much more confused, irregular, and difficult to be remembered, than those which we dream towards the morning; and these last are often rational to a considerable degree, and regulated according to the usual course of our associations. For the brain begins then to approach to the state of vigilance, or that in which the usual associations were formed and cemented. However, association has some power even in wild and inconsistent dreams.
Cor. I. As the prophecies were, many of them, communicated in the way of divine visions, trances, or dreams, so they bear many of the foregoing marks of dreams. Thus they deal chiefly in visible imagery; they abound with apparent impossibilities, and deviations from common life, of which yet the prophets take not the least notice: they speak of new things as of familiar ones: they are carried in the spirit from place to place; things requiring a long series of time in real life are transacted in the prophetical visions as soon as seen; they ascribe to themselves and others new names, offices, &c.; every thing has a real existence conferred upon it; there are singular combinations of fragments of visible appearances; and God himself is represented in a visible shape, which of all other things must be most offensive to a pious Jew. And it seems to me that these and such like criterions might establish the genuineness of the prophecies, exclusively of all other evidences.
Cor. II. The wildness of our dreams seems to be of singular use to us, by interrupting and breaking the course of our associations. For, if we were always awake, some accidental associations would be so much cemented by continuance, as that nothing could afterwards disjoin them; which would be madness.
Cor. III. A person may form a judgment of the state of his bodily health, and of his temperance, by the general pleasantness or unpleasantness of his dreams. There are also many useful hints relating to the strength of our passions deducible from them.