mental activity during the day. It will probably not be out of place here to give a synopsis of various conditions which may be recognised as sources of dreams.
The source of a dream may be:
(a) A recent and psychologically significant experience which is directly represented in the dream.[1]
(b) Several recent, significant experiences, which are united by the dream into a whole.[2]
(c) One or more recent and significant experiences, which are represented in the dream by the mention of a contemporary but indifferent experience.[3]
(d) A subjective significant experience (a recollection, train of thought), which is regularly represented in the dream by the mention of a recent but indifferent impression.[4]
As may be seen, in dream interpretation the condition is firmly adhered to throughout that each component of the dream repeats a recent impression of the day. The element which is destined to representation in the dream may either belong to the presentations surrounding the actual dream stimulus itself—and, furthermore, either as an essential or an inessential element of the same—or it may originate in the neighbourhood of an indifferent impression, which, through associations more or less rich, has been brought into relation with the thoughts surrounding the dream stimulus. The apparent multiplicity of the conditions here is produced by the alternative according to whether displacement has or has not taken place, and we may note that this alternative serves to explain the contrasts of the dream just as readily as the ascending series from partially awake to fully awake brain cells in the medical theory of the dream (cf. p. 64).
Concerning this series, it is further notable that the element which is psychologically valuable, but not recent (a train of thought, a recollection) may be replaced, for the purposes of dream formation, by a recent, but psychologically indifferent, element, if only these two conditions be observed: 1. That the dream shall contain a reference to something which has
