Tolerance of moral and religious views other than one’s own is often considered a civic virtue in the United States. In the Catholic moral tradition, however, the principle has a long history that is rooted not purely in a democratic conception of government, but of government as it is properly related to the common good. For example, St. Thomas Aquinas refers to the Principle of Toleration where he addresses the questions of whether or not every evil or vice should be repressed in every circumstance under human law (Summa Theologica I-II, Q. 96, A. 2) and whether or not those who govern should try to prevent every evil under every circumstance (Summa Theologica I-II, Q. 90, A. 2). As with the Principles of Double Effect, Integrity and Totality, and the Principles of Cooperation, the Principle of Toleration was developed as a set of moral criteria for discerning how to pursue good in a world in which evil is inevitable.
According to this principle, those who govern both society and the individual institutions that constitute important elements of the common good may at times—where prudence dictates—tolerate the evil actions of others (including some intrinsic evils), if two criteria are met: 1) if a greater good or set of goods would be lost if the evil action were not tolerated; or, 2) if greater evils would occur were the original evil not tolerated. The Principle of Toleration, however, should be not be considered a "loop hole" to the prohibition against formal and immediate material cooperation. In other words, the principle of toleration cannot justify an illicit participation in an intrinsically evil action, but only the toleration of others participating in evil actions where the eradication of this participation is not practically or morally feasible.
