The idea that the physiological position of the body reflects what the mind, especially the unconscious aspect of the mind, is considering. A typical example of this is the belief that if a person crosses their arms they are being defensive, have a lack of trust, and are closing themselves off to you. This idea was popularized in the book Body Language by Julius Fast and has spurred an enormous market. However, that book itself is a simplification of concepts originally presented in the book Kinesics and Context by Ray L. Birdwhistell. In that book, the author shows that individual or groups of body positions cannot be interpreted by themselves. Rather, the historic and social influences on a person should be taken into account before accurate interpretation can be made. It is this part of interpreting body language that is frequently omitted and that brings into question the validity of most interpretations.