Two different schools of thought exist as to why we dream: the physiological school, and the psychological school.

Both, however, agree that we dream during the REM, or rapid eye movement, phase of sleep. During this phase of sleep, our closed eyes dart rapidly about, our brain activity peaks, and our muscles suffer temporary paralysis.

The physiological theory centers upon how our body, specifically our brains, function during the REM phase of sleep. Proponents of this theory believe that we dream to exercise the synapses, or pathways, between brain cells, and that dreaming takes over where the active and awake brain leaves off. When awake, our brains constantly transmit and receive messages, which course through our billions of brain cells to their appropriate destinations, and keep our bodies in perpetual motion. Dreams replace this function.

Two underpinning physiological facts go towards supporting this theory of dreams. The first lies in the fact that the first two or so years of ones life, the most formative ones for learning, are also the ones in which the most REM sleep occurs. It follows that during this time of the greatest REM sleep, we experience the greatest number of dreams. The second physiological fact that lends credence to this theory is that our brain waves during REM sleep, as recorded by machines measuring the brain's electrical activity, are almost identical in nature to the brain waves during the hours we spend awake. This is not the case during the other phases of sleep.

Psychological theorists of dreams focus upon our thoughts and emotions, and speculate that dreams deal with immediate concerns in our lives, such as unfinished business from the day, or concerns we are incapable of handling during the course of the day. Dreams can, in fact, teach us things about ourselves that we are unaware of.

Connections between dreams that the human psyche have been made by many people over thousands of years. The famous Greek philosopher, Aristotle wrote in his "Parva Naturalia," over 2,200 years ago, of a connection between dreams, waking experiences, and emotional needs.

Others have delved into more complicated explanations for dreams, such as the prophetic nature of dreams written of in the Bible, which was and is a belief held by many cultures. Sigmund Freud, one of the fathers of modern psychology, believed dreams to be symbolic of any number of things buried deep within our minds and our memories.

Until someone proves or disproves one of these theories, or poses an alternate one, we are left at square one. Our knowledge as to what causes us to dream is limited to the fact that we do dream, and that dreams occur during the REM phase of sleep. Sweet dreams!