Section — Wouters, Manual of Moral Theology
VI. On the Participant
I. Notion and division. The participant is distinguished in two ways: participant in the thing and participant in the unjust action, according as he either buys or receives as a gift part of the thing offered, or helps the damager in inflicting damage (St. Alphonsus, III, 571).
II. Damages to be repaired. The participant in the thing is bound as an unjust possessor of another's thing; the participant in the unjust action must restore as an unjust damager, and indeed in proportion to his influence (St. Alphonsus, loc. cit.; n. 993 sq.).
Question. To what extent is it permitted, in order to avoid one's own damage, to cooperate in a damaging action? The discussion is about material cooperation, because formal cooperation is always illicit. Furthermore:
Response 1. To cooperate mediately in damage to one's neighbor is permitted for a proportionately grave cause. Thus it is permitted, for example, in order to avoid death, to hand over a sword to one who is going to kill another (St. Alphonsus, III, 571; n. 556).
Response 2. To cooperate immediately is permitted as follows:
It is not permitted to cooperate immediately in the killing or mutilation of another, because such cooperation is intrinsically evil (n. 556).
It is permitted for a grave cause to cooperate immediately in damage in goods of fortune: 1° if the cooperator has both the power and the will of repairing the damage to be inflicted; 2° if there is question of inflicting light damage; 3° if, cooperation being denied, the damage will nevertheless be inflicted by the principal author. The reason for all of these is that in the cases posited the one to be harmed is bound by charity to consent to the cooperation, so that injury ceases. Outside the enumerated cases it is not permitted to cooperate immediately, because the one to be harmed is not bound to consent, so that injury does not cease. Make exception if, from denied cooperation, some most grave evil threatens someone, for example death, mutilation, etc., because then the one to be harmed is again bound to consent; or even consent is not required, almost as if there is question of one who in extreme or quasi-extreme necessity can take another's goods, by which he averts most grave damage (St. Alphonsus, III, 571).
It is disputed whether in this last case the cooperator is bound to restitution. Others affirm, excepting the case in which the cooperator was absolutely poor, that is, poor in reality and in hope; just as one is bound who in extreme necessity took another's goods. But with St. Alphonsus it seems that the distinction must be made thus: the cooperator is not bound to restitution if he avoided damage of a higher order, for instance death, mutilation, grave infamy; he is bound if he avoided damage of the same order, that is, damage of fortune. The reason is that in the former case he did not spare his own goods, otherwise in the latter case (III, 571).