Introduced by Edwin Lemert in his Social Pathology (1951), the distinction is central to labelling theory. Primary deviation refers to differentiation which is relatively insignificant, marginal, and fleeting: individuals may drift in and out of it. Secondary deviation is deviance proper. It is a pivotal, central, and engulfing activity to which a person has become committed. The mechanism by which marginal deviance and casual rule-breaking become more central depends upon labelling or the societal reaction.