Chapter IV. On War

War is a fight of a multitude against a foreign multitude, for the sake of defending or vindicating the commonwealth. Hence it differs: 1st. from a brawl, which is a fight of a few against a few, and without authority, nor undertaken for the good of the commonwealth; 2nd. from sedition, which is a tumult or conflict of a multitude against the political society to which it belongs.

I say 1st. War is licit of itself, whether for repelling injury or for vindicating one's own right. The reason is that any society independent from another society ought to have a means of protecting itself against injury and of vindicating its own right; but sometimes no other means is available for obtaining this end except war. For since higher tribunals are lacking to which nations or Princes may have recourse, it remains only that, in order to obtain satisfaction from another society, they use war. - Cf. St. Thomas, 2-2, q. 40, art. 1.

I say 2nd. For a just and licit war, the following are necessarily required: 1st. legitimate authority, that is, supreme authority, acknowledging no other superior in civil matters, and the reason is that where a greater authority is had, this authority ought to judge concerning the dispute; 2nd. a just and grave cause, which is preponderant over the inconveniences that will follow from the war, e.g., a kingdom or province to be recovered, or a grave injury to the commonwealth to be repelled, or a rebellion of subjects to be repressed, etc.; 3rd. the due mode of waging war, namely that before war condign satisfaction be required from the adverse party; and if this is offered, it ought to be accepted as a matter of justice; for where war ceases to be necessary, it also ceases to be just. - Cf. St. Thomas, ibid.

You Will Ask. Can soldiers wage war with doubt concerning the justice of the war?

Response. If it concerns a subject soldier, or even a soldier hired before the war was declared, he can, indeed he ought to obey where the war is not evidently unjust, because in doubt one must stand for the superior. But if it concerns a soldier not yet hired, he is bound to inquire concerning the justice of the war, nor can he hire himself out in doubt concerning its justice. The reason is that no one can cooperate toward despoiling someone of a thing which he possesses, unless he is certain that it is unjustly possessed by him. - Cf. St. Alphonsus, n. 408.¹

¹ Cf. Addenda, p. 1112, n. 58.