Dreams have been considered significant for millennia. We read in the Old Testament about Joseph interpreting the dreams of Pharaoh, and of Jacob dreaming of a ladder to heaven; ancient Egyptians believed dreams were messages from the gods; ancient Greeks slept in sanctuaries of Asclepios and dreamed of cures to their illnesses.
The modern attitude towards the interpretation of dreams owes much to Sigmund Freud. Although many of his theories have fallen out of favor, dream interpretation would not exist as it does today if Freud hadn’t brought it into view. Freudian theory posits that every aspect of a dream is a symbol for some wrinkle in the dreamer’s subconscious.
Freud’s student, Carl Jung, preferred to interpret dreams not by their individual elements, but by the overall picture. Jung introduced the concept of the collective unconscious to dream theory: the idea that there are archetypes and ideas that exist in all our minds. It’s a tricky term — some people think of the collective unconscious as a mystical sort of connection between everyone, while others use it as a label for the shared images and ideas we acquire through our culture. (In other words, some people think that the reason you think “danger” when I say “wolf” is because we have an inherent, unconscious sense that wolves are dangerous; other people think that you think “danger” when I say “wolf” because our parents told us the story of Little Red Riding Hood when we were little.)
In 1952, Eugene Aserinsky defined a link between dreaming and the period of sleep called rapid eye movement sleep, or REM sleep. Dreaming seems to have something to do with cementing memories in our brains, and may serve as a way for our minds to sort out our experiences from the day. Scientists are constantly refining the information we have on the neurobiology of dreams — but their purpose is still something of a mystery.