Recognizing that natural law is the basis for and places limits on positive law means admitting that it is legitimate to resist authority should it violate in a serious or repeated manner the essential principles of natural law. Saint Thomas Aquinas writes that “one is obliged to obey ... insofar as it is required by the order of justice”.823Saint Thomas Aquinas, Summa Theologiae, II-II, q. 104, a. 6, ad 3um: Ed. Leon. 9, 392: “principibus saecularibus intantum homo oboedire tenetur, inquantum ordo iustitiae requirit”. Natural law is therefore the basis of the right to resistance. There can be many different concrete ways this right may be exercised; there are also many different ends that may be pursued. Resistance to authority is meant to attest to the validity of a different way of looking at things, whether the intent is to achieve partial change, for example, modifying certain laws, or to fight for a radical change in the situation.
The Church's social doctrine indicates the criteria for exercising the right to resistance: “Armed resistance to oppression by political authority is not legitimate, unless all the following conditions are met: 1) there is certain, grave and prolonged violation of fundamental rights, 2) all other means of redress have been exhausted, 3) such resistance will not provoke worse disorders, 4) there is well-founded hope of success; and 5) it is impossible reasonably to foresee any better solution”.824Catechism of the Catholic Church, 2243. Recourse to arms is seen as an extreme remedy for putting an end to a “manifest, long-standing tyranny which would do great damage to fundamental personal rights and dangerous harm to the common good of the country”.825Paul VI, Encyclical Letter Populorum Progressio, 31: AAS 59 (1967), 272. The gravity of the danger that recourse to violence entails today makes it preferable in any case that passive resistance be practised, which is “a way more conformable to moral principles and having no less prospects for success”.826Congregation for the Doctrine of the Faith, Instruction Libertatis Conscientia, 79: AAS 79 (1987), 590.