Placentinus the Jurist allowed private self-defense along ancient Roman lines (
vim vi defendere omnes leges omniaque iura permittunt), but, in combating the "blood-feud mentality" of his times, restricted it to the same time of the initial aggression--otherwise only sinful, primitive vendetta or revenge existed, not licit self-defense (
Summa Codicis).
Accursius the Italian Jurist emphasized moderation and proportionality as central to private self-defense. If the initial trespass was done weapon-less, the repulsion likewise must be weapon-less. Armed self-defense was conditionally legitimized as "moderate and fully legal" when the unjust initiator of violence introduced weaponized violence or terror (
Glossa Ordinaria). The "Romanist" position of Accursius based legitimacy of self-defense in private capacity purely on "proportionate moderation", yet completely banned vendettas or indiscriminate violence even in its empowerment of very strong right of private self-defense.
Simon of Bisagnano the Canonist was of the view that private self-defense existed by both human and Divine Law, and, provided it was done in "moderation," one could even strike back a cleric (
Summa).
The canon lawyer Raymond of Pennaforte stated: "
It is always lawful to meet force with force" (
Summa, Book II).
The main exception to "private" violence as unlawfulness in Catholicism is the "personal" or individually-mandated violence being belonging to the "exceptional ethical state" of extralegal, justifiable insurgency and, more particularly,
Tyrannicide.
In his
Policraticus, John of Salisbury effusively lauds private, personal executors of Higher Law against Tyrants, as Public Enemies, as unquestionably acting as agents of God, inflicting atypical yet true justice in full moral righteousness, and theologically unassailable.
John of Salisbury positively glorifies the martyric Tyrannicidal assassination of the anti-Christian Emperor Julian the Apostate by the Christian soldier-martyr Mercurius, who was acting under the dictation of the Blessed Virgin, according to the argument. Innumerable examples of Tyrannicidal Assassination are cited by John, both biblical, classical and contemporary. John asserts if a Ruler or Prince "
resists and opposes the divine commandments, and wishes to make me share in his war against God, then with unrestrained voice I must answer back that God must be preferred before any man on earth", and such a God-rebelling Ruler opens up the way for Tyrannicidal dissidence and Heaven-mandated individually-authorized deadly insurgent retribution.
John argues thus: "It is not only permitted, but it is also equitable and just to slay tyrants. For he who receives the sword deserves to perish by the sword. But ‘receives’ is to be understood to pertain to he who has rashly usurped that which is not his, not he who receives what he uses from the power of God. He who receives power from God serves the laws and is the slave of justice and right. He who usurps power suppresses justice and places the laws beneath his will. Therefore, justice is deservedly armed against those who disarm the law, and the public power treats harshly those who endeavor to put aside the public hand. And, although there are many forms of high treason, none is of them is so serious as that which is executed against the body of justice itself. Tyranny is, therefore, not only a public crime, but if this can happen, it is more than public. For if all men as prosecutors may be allowed in the case of high treason, how much more are they allowed when there is oppression of laws which should themselves command emperors? Surely one should punish a public enemy, and whoever does not prosecute him transgresses against himself and against the whole body of the earthly republic ... As the image of the deity, the prince is to be loved, venerated, and respected; the tyrant, as the image of depravity, is (for the most part even) to be killed... It is just for public tyrants to be killed and the people to be liberated for obedience to God" (
Policraticus).
No stronger statement of justification of individually-licensed deadly violence against usurping force could be vocalized, and no more courageous defense of the Natural and Divine Law be so protective of the continued preservation of the
Lex Naturalis in the realm of the State.
Azo the Roman Jurist likewise argued a Ruler's
imperium (as political power) was proportionate to his
iuridictio (legitimate authority); if a Ruler or King transgressed the boundaries of lawfulness and degenerated into a "
Rex Tyrannus", there existed an individually and personally-based moral right and duty of Tyrannicide.
St. Thomas Aquinas too, even implicitly allowed, on morally pragmatic grounds, for personally-based insurgency in circumstances of harsh Tyranny:
http://www.newadvent.org/summa/3042.htmA tyrannical government is not just, because it is directed, not to the common good, but to the private good of the ruler, as the Philosopher states (Polit. iii, 5; Ethic. viii, 10).
Consequently there is no sedition in disturbing a government of this kind, unless indeed the tyrant's rule be disturbed so inordinately, that his subjects suffer greater harm from the consequent disturbance than from the tyrant's government.
Indeed it is the tyrant rather that is guilty of sedition, since he encourages discord and sedition among his subjects, that he may lord over them more securely; for this is tyranny, being conducive to the private good of the ruler, and to the injury of the multitude.
In another work,
Scripta Super Libros Sententiarum, St. Thomas even goes even further and unabashedly ethically justifies full-blown extralegal, extra-judicial, informal, tacitly individually-authorized Tyrannicide:
[When no recourse to a morally-upright superior is juridically existent to the people], "
He who delivers his country by slaying a tyrant is to be praised and rewarded."
