Sigmund Freud was the founder of the psychoanalytic theory. His work had a profound influence on psychology, sociology, anthropology, literature, and even art.

Freud believed that behaviour and personality came from the interaction of conflicting psychological forces that works at three levels of awareness:

According to Freud, thoughts and emotions outside of our awareness continue to influence our behaviour, even if we are unaware of it. The unconscious can include repressed feelings, hidden memories, habits, thoughts, desires, and reactions.

The conscious and unconscious minds can be understood by what is known as a slip of the tongue.