The representative group falls into two subdivisions, according as the memories are of old or of recent date; these subdivisions are often quite distinct, recent dream memories belonging--probably with most people--to the previous day, while old dream memories are usually drawn from the experience of many years past, and frequently from early life. In the same way presentative impressions fall into two subdivisions, according as they refer to external stimuli present to the senses, or to internal disturbances within the organism. It is scarcely necessary to observe that any or all of these four sub-groups, into which the whole of our dream life may be analysed, may become woven together in the same dream. I have called the classification 'provisional' because, though it is convenient to adopt it for the sake of orderly arrangement, when we come to consider the matter it will be found that the material of dreams is in reality all of the same order, and purely psychic, though it may be differentiated in accordance with the character of the stimulus which evokes the psychic material of which it is made. Strictly speaking, the source of the dream as a dream can only be central, and a truly presentative dream is impossible. If our senses receive an impression, external or internal, and we recognise and accept that impression for what we should recognise and accept it when awake, then we cannot be said to be dreaming. The internal and external stimuli which act upon sleeping consciousness are not a part of that consciousness, nor in any real sense its source or its cause. The ray of sunlight that falls on the dreamer, the falling off of his bedclothes, the indigestible supper he ate last night--these things can no more 'account' for his dream than the postman's knock can account for the contents of the letter he delivers. Whatever the stimuli from the physical world that may knock at the door of dreaming consciousness, that consciousness is apart from them, and stimuli can only reach it by undergoing transformation. They must put off the character which they wear as phenomena of the waking world; they must put on the character of phenomena of another world, the world of dreams. FOOTNOTES: [Footnote 1: The subdued quality of the light in normal dreaming--the usual absence of sunshine and generally even of colour--has long been noted. 'We never dream of being in the sunshine,' says Henry Dircks (_Lancet_, 11th June 1870, p. 863), though too absolutely; 'light and shade form no requisite elements.... The liveliest and most impressive dream is, in reality, a true night scene, very dubiously lighted up, and in which the nearest objects are those which we principally observe and which most interest us.']