Meanwhile, a competing philosophy of prison management known as the "silent system" arose. The main distinguishing feature of this system was that prisoners were allowed to work together in the daytime. Silence was strictly enforced at all times, however, and at night the prisoners were confined in individual cells. Vigorous competition between supporters of the silent system and of the separate system prevailed until about 1850, but by that time the silent system had been victorious in most U.S. states.

The "mark system" was developed about 1840 by Captain Alexander Maconochie at Norfolk Island, an English penal colony located east of Australia. Instead of serving fixed sentences, prisoners there were required to earn marks or credits proportional to the seriousness of their offenses. Credits were accumulated through good conduct, hard work, and study, and could be denied or subtracted for indolence or misbehaviour. When a prisoner obtained the required number of credits he became eligible for release. The mark system presaged the use of indeterminate sentences, individualized treatment, and parole. Above all it emphasized training and performance, rather than solitude, as the chief mechanisms of reformation.

Further refinements in the mark system were developed in the mid-1800s by Sir Walter Crofton, director of Irish prisons. Irish inmates progressed through three stages of confinement before they were returned to civilian life. The first portion of the sentence was served in isolation. Then the prisoners were allowed to associate with other inmates in various kinds of work projects. Finally, for six months or more before release, the prisoners were transferred to "intermediate prisons," where inmates were supervised by unarmed guards and given sufficient freedom and responsibility to permit them to demonstrate their fitness for release. Release was also conditional upon the continued good conduct of the offender, who could be returned to prison if necessary.

Many features of the Irish system were adopted by reformatories constructed in the United States in the late 19th century for the treatment of youthful and first offenders. The leaders of the reformatory movement advocated the classification and segregation of various types of prisoners, individualized treatment emphasizing vocational training and industrial employment, indeterminate sentences and rewards for good behaviour, and parole or conditional release. The reformatory philosophy gradually permeated the entire U.S. prison system. The Irish system and the American innovations had great impact upon European correctional practices in the 20th century. There are several justifications for the use of incarceration in the criminal justice system. It is seen as an effective form of punishment, the threat of which serves as a deterrent to potential criminals. And by isolating a convicted offender for lengthy periods of time, society is thereby protected from the crimes he might have committed while free. Moreover, the controlled environment of a prison offers opportunities for the rehabilitation of criminals through counseling services, education, vocational training, and so on. These arguments assume that the isolation of the offender is not outweighed by the possibility of his becoming more criminal while in prison and that the social and economic costs of isolating the criminal from the rest of society are less than those incurred if he had been left free.

Jails, in the modem sense, are products of the last century. It is a legacy of British rule. E C Winese observed that, "the prison system in Indian Empire, like the British rule itself in that country, has grown up by degrees, until, as the empire was consolidated and order introduced into all departments of the Government, the treatment of criminals took its place among the recognized branches of the judicial administration'. H S Stratchey made a survey of jail accommodation throughout the territories of the East India Company in 1805. Before 1835, 'there were 43 civil, 75 criminal and 68 mixed jails' in the territories under the company".