numerous, but the safe application is difficult and attended with risk. The chief difficulty lies in determining the gravity of the cause which will justify one in co-operating materially in another's sin. No general rule can be laid down on the point beyond saying that a graver cause is required when there is question of a graver sin, when the co-operation is more proximate, and when it is more probable that the sin would not be committed at all if the co-operation were denied. The following examples taken from approved authors are given as illustrating the application of the doctrine, and they may be used to show what may be done in similar cases.
(a) I may lawfully ask for the sacraments from a bad priest, though he commits sin in administering them, for he need not sin thereby unless he likes, and his malice should not deprive me of the benefit of the sacraments to which I have a right.
(b) A dealer may sell to all buyers things which are in themselves indifferent, though they can be put to a bad use, as firearms, unless he is certain that they are required for a bad purpose. Even in the latter case a correspondingly serious inconvenience or loss will excuse his selling, especially if his refusal will not hinder the sin on account of the buyer being easily able to procure what he wants elsewhere.
(c) Intoxicating drink may not be sold to one who has already had too much. Many authors, however, allow this to be done when it cannot be refused without provoking to violence and quarrelling. This excuse would rarely avail in England at present, because the law forbids such sale, the strong arm of the law thus being on the side of morality.
(d) It is not lawful to sell things of which the use is ordinarily sinful, except when their lawful use is guaranteed. And so booksellers are not allowed to sell infidel or immoral books except to such as require them for good reasons and with the requisite permission. The same doctrine applies to drugs and instruments used for immoral purposes, as well as to poisons. Publishers, too, sin by publishing books which are dangerous to faith or morals. Compositors and others employed in printing should not work for firms which are known to publish bad books; as they are usually ignorant of the nature of the work which they help to bring out, their ignorance, the remoteness of their co-operation, and the ease with which other workmen can be found to supply their place, will ordinarily excuse them from sin if an odd bad book or two are published by an otherwise respectable firm.
