Back in the times of the Romans and the Greeks, many scientists strongly believed that dreams held prophetic powers that could warn people of alarming future events. Since then, numerous theories regarding dreams have been proposed, yet even after years and years of research, scientists are still unable to prove the theories definitively.

Sigmund Freud was a neurologist who performed psychoanalytic studies and discussed his theories about dreams in his book, The Interpretation of Dreaming. In the late 19th century, he put forth a new theory, stating that dreams are "centred around the notion of repressed longing - the idea that dreaming allows us to sort through unresolved, repressed wishes," according to Scientific American. He describes dreams as a way for humans to fulfill long-desired wishes without sharing those with the world. Manifest and latent contents are the two main components to his theory, with manifest content being the images apparent in dreams and latent content being the secret psychological message behind them.

Today's exceptionally advanced technology allows scientists to examine theories introduced years before. In 1977, psychologists Robert McClarley and J. Allan Hobson introduced a new theory known as activation-synthesis. The theory suggests that brain impulses combine "memories, emotions, and sensations," according to Health Guidance, and puts them together, oftentimes illogically and randomly. These psychologists argue that dreams lack a legitimate purpose, or at least any purpose that can be adequately tested in an empirical form. Similarly to Freud, they believe that some dreams can be beneficial in our daily lives; however, most dreams we have are random with no real meaning.

Some scientists believe in the threat simulation theory, which states that dreams, or rather nightmares, began as an ancient defense mechanism from perceived threats around us. This ascribes dreams the purpose of defending ourselves from events or figures that we see as dangerous. Dreams were considered an evolutionary advantage due to their "capacity to repeatedly simulate threatening events," according to the National Center for Biotechnology Information. It supposedly creates more successful reproduction due to the fact that over time human genes will develop threat cues and avoidance.

The most promising theory that may explain why we dream is the cognitive theory studied by David Foulkes. According to Macalester College, this theory proposes that dreams merge knowledge already stored in our brains and form connections between them. Dreams resemble a puzzle, where scattered pieces of information bind together in a dream to form a clearer image that helps humans problem-solve. Ultimately, these scientists believe that dreams make us more conscious of our choices due to new knowledge collected from dreams.

Perhaps the purpose of dreams may require further scientific research and empirical evidence. Despite the uncertainty, scientists continue to study their purpose using the work of earlier psychoanalysts, such as Sigmund Freud, along with previously tested theories.