During the epoch which may be described as pre-scientific, men had no difficulty in finding an explanation of dreams. When they remembered a dream after waking up, they regarded it as either a favourable or a hostile manifestation by higher powers, daemonic and divine. When modes of thought belonging to natural science began to flourish, all this ingenious mythology was transformed into psychology, and to-day only a small minority of educated people doubt that dreams are a product of the dreamer‘s own mind.

Since the rejection of the mythological hypothesis, however, dreams have stood in need of explanation. The conditions of their origin, their relation to waking mental life, their dependence upon stimuli which force their way upon perception during the state of sleep, the many peculiarities of their content which are repugnant to waking thought, the inconsistency between their ideational images and the affects attaching to them, and lastly their transitory character, the manner in which waking thought pushes them on one side as something alien to it, and mutilates or extinguishes them in memory - all of these and other problems besides have been awaiting clarification for many hundreds of years, and till now no satisfactory solution of them has been advanced. But what stands in the foreground of our interest is the question of the significance of dreams, a question which bears a double sense. It enquires in the first place as to the psychical significance of dreaming, as to the relation of dreams to other mental processes, and as to any biological function that they may have; in the second place it seeks to discover whether dreams can be interpreted, whether the content of individual dreams has a ‘meaning‘, such as we are accustomed to find in other psychical structures.