What Exactly Is a Dream?

Dreams are a curious phenomenon, and the experience of dreaming is universal. Yet across human cultures, ancient and modern, dreams have remained mysterious. In many traditional tribal societies, dreams are often seen as divine messages or the work of spirits—which is not surprising. Even in modern, highly developed societies, superstitions about dreams persist.

In traditional Chinese culture, countless stories revolve around dreams. Zhuangzi’s butterfly dream, the Handan dream, the tale of a brush that produces flowers in a dream, Jiang Lang’s creative drought, and the Nanke dream are all well-known. However, ideas about dreams have long differed between China and the West. The Greek philosopher Plato once said, "Good people dream, while bad people do evil." By contrast, early Chinese thinkers believed that "the sage has no dreams." A sage—an enlightened person—is thought to have no idle thoughts, and therefore does not dream. From the perspective of modern psychology, both Eastern and Western antiquity misunderstood dreams in many ways. Contemporary psychologists hold that, regardless of whether one is good or bad, wise or foolish, everyone dreams—and even animals dream. This is evidenced by the rapid eye movements observed in sleeping animals (watch a sleeping dog, for instance). The difference is that animals cannot recount their dreams upon waking, as humans can.

  In psychology, dreams are spontaneous mental activity that occurs during specific stages of sleep. The entire process of the physical and psychological changes an individual undergoes during this activity is called dreaming.

• On a typical night, a person’s first dream usually occurs about 90 minutes after falling asleep. Each dream lasts roughly 5-15 minutes (around 10 minutes on average), and dreams recur across different sleep stages throughout the night, with about 4-6 dreams in total; altogether, roughly 1-2 hours of sleep time is spent dreaming.
• Why do we have 4-6 dreams each night but remember only a few upon waking?

There are three different perspectives on this question:

• Interference theory: multiple dreams interfere with one another, and the most recent may overshadow earlier ones; although dreams can occur throughout the night, people often remember only the last dream before waking. This explanation generally aligns with common experience.
• Motivated forgetting: it posits that dreams often involve unpleasant events, which people do not remember to avoid anxiety. However, this does not fit the facts, as most people do not remember only pleasant dreams.
• Information-processing theory: dreaming unfolds within short time frames and essentially functions like short-term memory. If short-term memories are not rehearsed or transferred into long-term storage, they are quickly forgotten. This explanation emerged with the rise of cognitive psychology and seems more reasonable.