The forgetting of dreams is treated in the most detailed manner by Strümpell. This forgetting is evidently a complex phenomenon; for Strümpell does not explain it by a single reason, but by a considerable number of reasons.
In the first place, all those factors which produce forgetfulness in the waking state are also determinant for the forgetting of dreams. When awake we are wont soon to forget a large number of sensations and perceptions because they are too feeble, and because they are connected with a slight amount of emotional feeling. This is also the case with many dream pictures; they are forgotten because they are too weak, while stronger pictures in proximity will be remembered. Moreover, the factor of intensity in itself is not the only determinant for the preservation of the dream pictures; Strümpell, as well as other authors (Calkins), admits that dream pictures are often rapidly forgotten, although they are known to have been vivid, whereas among those that are retained in memory there are many that are very shadowy and hazy. Besides, in the waking state one is wont to forget easily what happened only once, and to note more easily things of repeated occurrence. But most dream pictures are single experiences, and this peculiarity equally contributes towards the forgetting of all dreams. Of greater significance is a third motive for forgetting. In order that feelings, presentations, thoughts and the like, should attain a certain degree of memory, it is important that they should not remain isolated, but that they should enter into connections and associations of a suitable kind. If the words of a short verse are taken and mixed together, it will be very difficult to remember them. "When well arranged in suitable sequence one word will help another, and the whole remains as sense easily and firmly in the memory for a long time. Contradictions we usually retain with just as much difficulty and rarity as things confused and disarranged." Now dreams in most cases lack sense and order. Dream compositions are by their very nature incapable of being remembered, and they are forgotten because they usually crumble together the very next moment. To be sure, these conclusions are not in full accord with the observation of Radestock (p. 168), that we retain best just those dreams which are most peculiar.
According to Strümpell, there are still other factors effective in the forgetting of dreams which are derived from the relation of the dream to the waking state. The forgetfulness of the waking consciousness for dreams is evidently only the counterpart of the fact already mentioned, that the dream (almost) never takes over successive memories from the waking state, but only certain details of these memories which it tears away from the habitual psychic connections in which they are recalled while we are awake. The dream composition, therefore, has no place in the company of psychic successions which fill the mind. It lacks all the aids of memory. "In this manner the dream structure rises, as it were, from the soil of our psychic life, and floats in psychic space like a cloud in the sky, which the next breath of air soon dispels" (p. 87). This is also aided by the fact that, upon awakening, the attention is immediately seized by the inrushing sensory world, and only very few dream pictures can withstand this power. They fade away before the impressions of the new day like the glow of the stars before the sunlight.
As a last factor favouring the forgetting of dreams, we may mention the fact that most people generally take little interest in their dreams. One who investigates dreams for a time, and takes a special interest in them, usually dreams more during that time than at any other; that is, he remembers his dreams more easily and more frequently.
Two other reasons for the forgetting of dreams added by Bonatelli (given by Benini) to those of Strümpell have already been included in the latter; namely, (1) that the change of the general feeling between the sleeping and waking states is unfavourable to the mutual reproductions, and (2) that the different arrangement of the presentation material in the dream makes the dream untranslatable, so to speak, for the waking consciousness.
It is the more remarkable, as Strümpell observes, that, in spite of all these reasons for forgetting the dream, so many dreams are retained in memory. The continued efforts of the authors to formulate laws for the remembering of dreams amounts to an admission that here too there is something puzzling and unsolved. Certain peculiarities relating to the memory of dreams have been particularly noticed of late, e.g., that a dream which is considered forgotten in the morning may be recalled in the course of the day through a perception which accidentally touches the forgotten content of the dream (Radestock, Tissié). The entire memory of the dream is open to an objection calculated to depreciate its value very markedly in critical eyes. One may doubt whether our memory, which omits so much from the dream, does not falsify what it retained.
Such doubts relating to the exactness of the reproduction of the dream are expressed by Strümpell when he says: "It therefore easily happens that the active consciousness involuntarily inserts much in recollection of the dream; one imagines one has dreamt all sorts of things which the actual dream did not contain."
Jessen (p. 547) expresses himself very decidedly: "Moreover we must not lose sight of the fact, hitherto little heeded, that in the investigation and interpretation of orderly and logical dreams we almost always play with the truth when we recall a dream to memory. Unconsciously and unwittingly we fill up the gaps and supplement the dream pictures. Rarely, and perhaps never, has a connected dream been as connected as it appears to us in memory. Even the most truth-loving person can hardly relate a dream without exaggerating and embellishing it. The tendency of the human mind to conceive everything in connection is so great that it unwittingly supplies the deficiencies of connection if the dream is recalled somewhat disconnectedly."
The observations of V. Eggers, though surely independently conceived, sound almost like a translation of Jessen's words: "...L'observation des rêves a ses difficultés spéciales et le seul moyen d'eviter toute erreur en pareille matière est de confier au papier sans le moindre retard ce que l'on vient d'éprouver et de remarquer; sinon, l'oubli vient vite ou total ou partiel; l'oubli total est sans gravité; mais l'oubli partiel est perfide; car si l'on se met ensuite à raconter ce que l'on n'a pas oublié, on est exposé à compléter par imagination les fragments incohérents et disjoints fourni par la memoire...; on devient artiste à son insu, et le récit, periodiquement répété s'impose à la créance de son auteur, qui, de bonne foi, le présente comme un fait authentique, dûment établi selon les bonnes méthodes..."
Similarly Spitta, who seems to think that it is only in our attempt to reproduce the dream that we put in order the loosely associated dream elements: "To make connection out of disconnection, that is, to add the process of logical connection which is absent in the dream."
As we do not at present possess any other objective control for the reliability of our memory, and as indeed such a control is impossible in examining the dream which is our own experience, and for which our memory is the only source, it is a question what value we may attach to our recollections of dreams.
(e) The Psychological Peculiarities of Dreams.—In the scientific investigation of the dream we start with the assumption that the dream is an occurrence of our own psychic activity; nevertheless the finished dream appears to us as something strange, the authorship of which we are so little forced to recognise that we can just as easily say "a dream appeared to me," as "I have dreamt." Whence this "psychic strangeness" of the dream? According to our discussion of the sources of dreams we may suppose that it does not depend on the material