Dr. Sigmund Freud developed the psychoanalytic theory that states that there are three levels of consciousness. These three levels are known as the unconscious, pre-conscious and conscious.
The conscious mind stores the things that a person is aware of. It is the level that allows the ability to process what is going on around a person, and allows the person to reason and rationalize. It holds current thoughts and feelings and allows verbalization of these things.
The pre-conscious mind holds basic memories, those that are not at the forefront of the mind but which can be easily accessed at any time. Memories that are repressed or blocked are not included in this part of the consciousness. This level also includes the things a person is aware of but is not currently paying attention to, such as everyday surroundings.
The subconscious mind is where things such as repressed memories, needs and urges, fears, anxieties, ideas and conflicts tied to discomfort are stored. Traumatic experiences from the past, sexual needs and fantasies, and deep fears and phobias are all part of the subconscious mind and are not easy to access.
Freud suggested that this part of consciousness affects behavior and actions in ways that are not generally realized. Dr. Freud likened the three levels to an iceberg, with the subconscious being the most submerged part.