Question III: By whom war may be waged

First it is certain that Clerics constituted in sacred orders, and monks even if Laymen, are prohibited by ecclesiastical law. Concerning Monks it is had in the canon Eos qui, d. 20, question 3. Concerning Clerics, 23, question 8, especially the canon Clerici, and the canon Quicunque ex clero. So D. Thomas and others.

That these, however, can fight by the license of the Pontiff in a case of necessity, Covarruvias notes Relectio on the Clementine si furiosus, Bannes article 2, Cajetan in the same place, Valentia point 4.

The reason is; because then the ecclesiastical law yields to the natural obligation. Yet the cited Canons do not forbid clerics to be present, to exhort, to help with spiritual aids. See D. Thomas article 2, Valentia at the place cited, Molina disputation 108, Suarez tomus 5, disputation 47, section 6, Tannerus number 80.

Therefore if Clerics fight without due justice and license, they become irregular, as is gathered from the chapter De caetero, extra on homicide, provided that someone is there killed.

Indeed, even if they merely exhort in an unjust war, it is gathered from the chapter Quod in dubiis, extra on penalties, and the chapter Clericus, extra on homicide.

Therefore if Clerics fight in a just war by the Pope's license, even if they kill, they do not become irregular.

But if they fight in a just war, yet without license, they still do not incur irregularity, according to the common opinion — Sylvester under the word Bellum, question 3, 2, Covarruvias at the place cited, part 2, § 3, number 9, Castro book 2 on the penal law, chapter 14, Valentia at the place cited, point 4.

The reason is, because odious laws are not to be extended. Laws burden with irregularity only illicit homicide and the killing of public ministers of justice.

Nor is it credible that on account of an act to which one is bound by the law of nature one should incur an impediment to one's own office.

You will ask, at what time war is lawful. This is asked on account of feast days; it is certain, indeed, that on these days defensive war is lawful, as is had in 1 Machab. 2. It is proved: for if it is lawful to draw the ox out of the pit, as is said in Luke 14, and to heal a man, as is said in John 7, why would it not be lawful to fight for the preservation of the Republic? So Nicholas also decrees, the canon si nulla, 23, question 8.

It is also lawfully done when it is necessary to the end of the war, namely to victory. This the aforesaid Nicholas affirms, that with urgent necessity it is lawful.

It is nevertheless not a mortal sin, outside necessity, to fight on a feast day, provided Mass is heard, as Cajetan says, according to Valentia and Tannerus number 87, adducing Bannes here, and Molina disputation 111.