Ours is the century of the private dream. In the wake of Sigmund Freud's Die Traumdeutung (1900), we have learned to read our night-time experiences psychologically, as expressions of our intimate thoughts and desires. Even though Freud's theories have been extensively modified and deeply challenged, and various post-Freudian schools now argue vehemently over the “proper” way to read dreams, we have largely followed Freud in his suggestion that the dream is the “royal road to … the unconscious”.

Recently, researchers working on the physiology of sleep and dreams have challenged the dominant psychological, and particularly psychoanalytic, theories of dreaming – but in such a way as to confine the dream even more strictly to a realm governed by internal human process. In 1977, in an influential and controversial paper, J. Allan Hobson and Robert W. McCarley proposed that “the primary motivating force for dreaming is not psychological but physiological,” and that “the dream process” has “its origin in sensorimotor systems, with little or no primary ideational, volitional, or emotional content.” While careful not to deny dreams meaning, Hobson and McCarley do seriously delimit the scope of the dream's significance. Dreaming becomes for them not Freud's “royal road,” but a much reduced “royal road to the mind and brain in a behavioral state, with different rules and principles than during waking.”

Following on from such physiological work as Hobson and McCarley's, other researchers have denied that dreams can, or should, be interpreted.