A lucid dream is any dream in which one is aware that one is dreaming. In relation to this phenomenon, Greek philosopher Aristotle observed: "often when one is asleep, there is something in consciousness which declares that what then presents itself is but a dream". One of the earliest references to personal experiences with lucid dreaming was by Marie-Jean-Léon, Marquis d'Hervey de Saint Denys. Skeptics of the phenomenon suggest that it is not a state of sleep, but of brief wakefulness. Others point out that there is no way to prove the truth of lucid dreaming other than to ask the dreamer. Lucid dreaming has been researched scientifically, with participants performing pre-determined physical responses while experiencing a lucid dream. Scientific history Philosopher Norman Malcolm's 1959 text Dreaming had argued against the possibility of checking the accuracy of dream reports. Hearne's results were not widely distributed. Initiation REM sleep.