(b) Formal cooperation is from its nature opposed to charity; for charity disapproves of the sins of others and strives to prevent them, while formal cooperation, on the contrary, approves and assists the sins of others.
(c) Formal cooperation is also opposed to the virtue violated by the sin of the principal agent, in so far as the will of the cooperator delights in or approves of the circumstance of help given to the sin of the other (see 1468). Thus, if one opens the door to a caller whom one suspects to be a burglar and at the same time mentally sympathizes with the act of burglary, one is guilty in will of the act one approves.
(d) Formal cooperation as to its external act is opposed to the virtue violated by the cooperator, when the external act has a malice of its own. Thus, if one swears falsely in order to conceal the presence of a burglar hidden in the house, one is guilty of perjury; if one disobeys the laws of the Church by marrying clandestinely, one is guilty of disobedience; if one scandalizes third parties by cooperating with sin, one is guilty of scandal; if one shares in fraud, one is guilty of injustice, etc. Hence, in confession it does not suffice to say that one has cooperated in sin, but one must also tell the sin committed and the necessary circumstances.
1514. The Sinfulness of Material Cooperation.—(a) Material cooperation, in itself, is sinful; for charity commands that one strive to prevent the sin of another, and much more therefore does it forbid one to help in the sin of another. (b) Material cooperation, in case of great necessity, is not sinful; for charity does not oblige under serious inconvenience to self, and it does not forbid one to cooperate by an indifferent act to prevent a neighbor from committing a greater evil than the evil he has in mind. He who cooperates materially through necessity does not cause sin, but uses his own right, which the bad will of the other abuses and makes an occasion of sin (see 1447 d).
1515. Lawfulness of Material Cooperation.—The conditions necessary in order that material cooperation be lawful are the same as for any other act that has a double result (see 104); for from the cooperation follow two results, one that is bad (viz., the sin of the other person) and one that is good (viz., the avoidance of loss or the retention of good). Two of the conditions required in the principle of double result need not be considered, however, since their presence is manifestly assured by the very fact that the cooperation is merely material. (a) Thus, the condition that the good effect must not be secured through the evil effect is verified; for, if one intends the sin of the other party as a means to the good end, cooperation is formal. Hence, if Balbus helps Claudius to get sinfully drunk, so that Claudius may go to confession the sooner, the cooperation of Balbus in the drunkenness of Claudius is formal. (b) The condition that the evil effect is not intended is also verified; for the very definition of material cooperation excludes the intention of the sin committed by the other party.
1516. Hence, we may confine our attention to the two remaining conditions stated in the principle of double effect, and conclude that material cooperation is lawful when and if the act of the cooperator is itself good or indifferent, and he has a reason sufficiently weighty for permitting the sin of the other party.
1517. The first condition of material cooperation is that the act of the cooperator must be good or at least indifferent; for, if it is evil, the cooperation becomes implicitly formal. But, since it is often difficult to determine in particular instances whether cooperation is intrinsically evil or merely indifferent, one must examine the nature and circumstances of the act.
(a) Thus, according to its nature, an act of cooperation is intrinsically evil, if it has no uses except such as are evil; it is indifferent, if, according to the intention of those who use it, it is now good, now evil. Hence, it is intrinsically wrong to assist in the manufacture or distribution of obscene books or pictures, or of drugs or instruments used exclusively for immoral purposes, since the only use to which such things can be put is sinful. It is also intrinsically wrong to take part even remotely in pagan superstitions, or to give any immediate assistance to an act which from its nature is opposed to the Sixth Commandment. But it is not intrinsically wrong to assist in the manufacture of firearms or poisons, which have many good uses, or to act as bodyguard to a person who fears harm from others.
(b) According to its circumstances, an act of cooperation is evil, if by reason of adjuncts it is wrong, as when it signifies approval of evil, gives scandal to others, endangers the faith or virtue of the cooperator, or violates a law of the Church. Thus, it is not from the nature of the act wrong to invite a pedestrian to ride in one’s car; but it is wrong from the circumstances when the pedestrian asks to be taken to a spot where he intends to commit robbery. It is not wrong intrinsically to work at building a temple; but it is wrong from the circumstances, when this act is regarded by the public as a sign of adherence to a false religion, or when the act causes scandal (see 983). The laws of the Church on mixed marriage or neutral schools afford other examples of cooperation lawful in one set of circumstances, but unlawful in another on account of significance, scandal, danger, etc.
1518. But the circumstance that the cooperator knows for certain that the principal agent will use the cooperation for sinful purposes, or will take scandal to the extent of being strengthened in his evil designs by reason of the assistance given, does not necessarily make cooperation evil.