Generally, for every month of satisfactory conduct，a certain number of days is deducted from the inmate's sentence. A usual procedure is to deduct one month from the first year of satisfactory conduct, two months for the second year，and so on, up to six months for the sixth and each succeeding year. A three-year sentence can thus be reduced to two years and six months by good behavior ；a ten-year sentence can be reduced to six years and three months. A prison board determines whether or not the prisoner has earned the reduction in time，but the legislature makes the schedule of reductions in time. Granting 'time off for good behavior' differs, in this respect，from commutation of sentence by executive order, in which the sentence is shortened because the inmate's behavior has been good, or for other reasons. ” Cf. H. L. A. Hart，Punishment and Responsibility，at p. 91 , Clarendon Press (1982 ).
[2]“In addition to statutory good time, as the general system is called by inmates,prisoners in some states may earn merit good time for extraordinary behavior and industrial good time for participation in the prison industries. ” Id. at p. 91.
[3] " Commutation of sentence is a reduction of the penalty by executive order. Commutation differs from conditional pardon in that it does not wipe away guilt in the eyes of the law, and consequently does not restore civil rights as does a pardon. Massachusetts governors commuted to life imprisonment 50 percent of the death sentences imposed by juries and courts from 1947 to 1971." Id. at p. 89.