According to St. Thomas (II-II, Q. liii, a. 1) scandal is a word or action evil in itself, which occasions another's spiritual ruin. It is a word or action, that is either an external act—for an internal act can have no influence on the conduct of another—or the omission of an external act, because to omit what one should do is equivalent to doing what is forbidden; it must be evil in itself, or in appearance; this is the interpretation of the words of St. Thomas: minus rectum. It is not the physical cause of a neighbor's sin, but only the moral cause, or occasion; further, this moral causality may be understood in a strict sense, as when one orders, requests, or advises another to commit the sin (this is strictly inductive scandal, which some call co-operation in a broad sense), or in a large sense, as when a person without being directly concerned in the sin nevertheless exercises a certain influence on the sin of his neighbor, e.g. by committing such a sin in his presence (this is inductive scandal in a broad sense). For scandal to exist it is therefore essential and sufficient, with regard to the nature of the act and the circumstances under which it takes place, that it be of a nature to induce sin in another; consequently it is not necessary that the neighbour should actually fall into sin; and on the other hand, for scandal strictly so-called, it is not enough that a neighbour take occasion to do evil from a word or action which is not a subject of scandal and exercises no influence on his action; it must be a cause of spiritual ruin, that is of sin, consequently that is not scandal which merely dissuades the neighbour from a more perfect act, as for instance, prayer, the practice of the Evangelical virtues, the more frequent use of the sacraments, etc. Still less can that be considered scandal, which only arouses comment, indignation, horror etc., for instance blasphemy committed in the presence of a priest or of a religious; it is true that the act arouses indignation and in common parlance it is often called scandalous, but this way of speaking is inaccurate, and in strictly theological terminology it is not the sin of scandal. Hence scandal is in itself an evil act, at least in appearance, and as such it exercises on the will of another an influence more or less great which induces to sin. Furthermore, when the action from which another takes occasion of sin is not bad, either in itself or in appearance, it may violate charity (see below), but strictly speaking it is not the sin of scandal. However, some authorities understanding the word scandal in a wider sense include in it this case
(1) Scandal is divided into active and passive. Active scandal is that which has been defined above; passive scandal is the sin which another commits in consequence of active scandal. Passive scandal is called scandal given (scandalum datum), when the act of the scandalizer is of a nature to occasion it; and scandal received (acceptum), when the action of the one who scandalizes is due solely to ignorance or weakness—this is scandal of the weak (infirmorum),—or to malice and evil inclinations—this is pharisaical scandal, which was that of the Pharisees with regard to the words and actions of Christ.
(2) Active scandal is direct when he who commits it has the intention of inducing another to sin; such is the sin of one who solicits another to the crime of adultery, theft etc. If one prevails upon another to commit the sin not only because of an advantage or pleasure believed to accrue therefrom but chiefly because of the sin itself, because it is an offence to God or the ruin of a neighbor's soul, direct scandal is called by the expressive name of diabolical scandal. On the other hand scandal is only indirect when without the intention to cause another to fall into sin we say a word or perform a deed which is for him an occasion of sin
(1) That active scandal is a mortal sin Christ Himself has taught (Matthew 18:6 sqq.) and reason makes evident. If charity obliges us to assist our neighbor's temporal and spiritual necessities (see ALMS; CORRECTION) it obliges us still more strongly not to be to him a cause of sin or spiritual ruin. Hence it follows that every sin of scandal is contrary to charity.
Moreover (2) direct scandal is obviously contrary to the virtue against which another is induced to sin; in fact every virtue forbids not only its violation by ourselves but also that we should desire its violation by another.
(3) Indirect scandal is also contrary to charity (see above); but is it also opposed to the virtue violated by another? St. Alphonsus answers in the affirmative; others, and this seems the true opinion, deny this. In fact no one has hitherto proved this species of malice, and those who admit it are not consistent with themselves, for they should also maintain, which no one does, that anyone who is indirectly the cause of an injustice by another is also bound to restitution; what is true of justice should hold good for the other virtues.
Cases in which the sin of scandal occurs
The question remains: When is there a sin of scandal? for it is obvious not all who an occasion of sin to others are thereby guilty.
(1) As a general rule the sin of scandal exists when one directly induces another to do a thing which he cannot do without sin, either formal or material, e.g. by soliciting a person to perjury, drunkenness, sins of the flesh, etc., even though the person induced to this act is habitually or at the time disposed to commit it. It is otherwise when the thing we ask is good or indifferent; this may be done without scandal and without sin, when there is a just cause or serious reason for asking it; even though one foresees that the other will probably sin in granting it; thus for the common weal a judge may demand an oath even from those who will probably commit perjury; one who has need of money and who cannot find anyone who will lend to him may have recourse to an usurer although he foresees that the latter will exact exorbitant and unjust interest, etc. The thing asked must be without sin either formal or material because it is not allowed to profit by the ignorance of another to induce him to commit what is forbidden, to cause a child to utter blasphemies, to induce someone who is unaware of the precept of the Church to eat flesh on a fast day and so on. In fact in all these cases the sin is to be ascribed to the person who endeavors to cause it This is the general rule, but here the question arises, may one advise another bent on committing a great crime to be satisfied instead with doing something less evil? This question is much discussed, but the opinion which considers such a course justifiable is probable and may be followed in practice. In fact the advice thus given is not properly speaking advice to do evil but to do a lesser evil or rather not to do the greater evil which a man intends to commit; therefore some writers exact that the words or circumstances must demonstrate that one advises the evil solely as the lesser evil; others, however, consider it sufficient that such be the intention, even when not made manifest, of the person who gives the advice. Nevertheless, if a man had decided to do an injury to a certain person one could not—unless in exceptional circumstances—induce him to do a lesser injury to any other person.
(2) He is guilty of the sin of scandal who without positively pledging or inducing to sin nevertheless performs an act evil in itself which will be an occasion of sin to another. The same must be said when the act is evil only in appearance, unless there be sufficient reason to act and to permit the fault of another Thus those who blaspheme before others when they foresee that their example will cause the latter to blaspheme are guilty of scandal; so also those who attack religion or morals, hold immoral conversation, sing immoral songs or (by their behaviour dress, writings etc.) offend against the laws of decency and modesty, when they foresee, as is usual, that those who see, hear, or read will be impelled to sin.
(3) To prevent another's sin one may even be bound to forego an act which is sinful neither in itself nor in appearance, but which is nevertheless the occasion of sin to another, unless there be sufficient reason to act otherwise. It has already been shown that when there is a just cause we may ask of another a thing which he can do without sin although we may foresee that he will not do it without fault. Likewise we are not bound to be disturbed by pharisaical scandal, which may follow an action we perform; but we must avoid scandalizing the weak if we can do so easily. The application of these principles depends on concrete circumstances, which vary with each case; however, the following general rules may be given:
To prevent scandalizing another we must never transgress the negative precepts of the natural law, nor its positive precepts in cases where they truly bind; thus it is not permitted to lie to prevent a mortal sin, neither can one neglect receiving baptism to avoid the blasphemies of one's parents.
It is not permitted to pass over any precept whatever in order to prevent pharisaical scandal, but we may and even should, in special cases and for one or two occasions, pass over a precept whether Divine or human, to avoid scandalizing the weak.
We should, to avoid scandal, forego good or indifferent works which are not of precept, if we can do so without great inconvenience.
Finally, to prevent the scandal of the weak we are sometimes obliged to sacrifice some temporal good of less importance, but we are not bound to do this when the goods are of greater importance.