Differential association theory (DAT) survived relatively untouched for several decades until the work of Ronald Akers in the 1960s. In particular, Akers added differential reinforcement to DAT to form a more comprehensive social learning theory (SLT) of criminal behavior or what was originally called differential association-reinforcement theory. SLT consisted of four main principles. The first two – differential association, and definitions – were borrowed almost directly from Sutherland. People learn definitions favorable or unfavorable to criminal behavior from those with whom they associate and people associate with different peers. Akers added differential reinforcement to get at why someone might continue or desist from criminal activity. People also learn through imitations. Social learning theory at the micro and macro levels as well as expansion of the theory to include social and biological factors by criminologists and Akers himself have become prominent in theorizing about crime today.