The theory itself incorporates many

The theory itself incorporates many important motivational concepts
previously identified in the literature with the notion of the self-concept.
Through their examination of the work of theorists such as Barnard (1938),
deCharmes (1968), Deci (1975), Etzioni (1961), Hackman and Oldham
(1976), Katz and Kahn (1978), Kelman (1980), Locke and Henne (1986),
Shamir (1990) and others, Leonard et al. (1999) identified three main
motivational concepts, which they labeled intrinsic process motivation, goal
internalization motivation, and instrumental motivation.