This paper studies optimal law enforcement in a model featuring preventive and non-preventive enforcement. Non-preventive enforcement is aimed at detecting and punishing offenders, while preventive enforcement seeks to prevent potential offenders from carrying out illegal actions (for example, officers on patrol can physically prevent crimes in progress, such as thefts or assaults). The deterrent effect of preventive enforcement is greater than that of non-preventive enforcement when it successfully deprives offenders of illicit gains and punishes them. However, preventive enforcement averts not only inefficient offenses but also efficient ones; as a result, it will be inferior to non-preventive enforcement in circumstances in which the available sanctions are high, enforcement is cheap, and a sufficient number of offenses are socially efficient. In our set-up, one potential outcome is that as available sanctions increase, enforcement efforts also increase, while deterrence remains unchanged (because there is less preventive enforcement). Finally, we show that in a framework with preventive enforcement, imprisonment need not be maximal, in contrast to the standard finding reported in the literature.
