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,
