We naturally think of dreams as experiences very like perceptions or imaginings, except that they occur during sleep. In prescientific thought the interpretation of dreams played a role in divining the future, and it plays a role, albeit a much more limited one, in modern psychology (although in Freudian psychoanalysis dreams have been considered to give access to some of the hidden operations of the mind). Dreaming is puzzling in many respects. We do not have ready-to-hand criteria for checking dream reports, not even our own; conscious or lucid dreams are the exception rather than the rule; and there is the puzzle of how we distinguish waking experience from a very lifelike dream. Furthermore, the nature of dreams is doubtful – some have even denied that to dream is to undergo an experience during sleep: dreams on this view are to be understood in terms of what happens when we ’recall’ them.