This is an entry in the Resources series.
Entries in this series will be more dry and technical, not building toward any particular conclusion – but they will also be very useful, laying down and unpacking foundations that will have a wide range of applicability to many arguments in the future.
In the Catechism of the Catholic Church, the word scandal is defined and unpacked in paragraphs 2284-2287 (note: here not quoted fully, but only in most relevant part):
CCC 2284: Scandal is an attitude or behavior which leads another to do evil. The person who gives scandal becomes his neighbor's tempter. He damages virtue and integrity; he may even draw his brother into spiritual death.
CCC 2285: Scandal… prompted our Lord to utter this curse: "Whoever causes one of these little ones who believe in me to sin, it would be better for him to have a great millstone fastened round his neck and to be drowned in the depth of the sea." [Matthew 18:6] Scandal is grave when given by those who by nature or office are obliged to teach and educate others. Jesus reproaches the scribes and Pharisees on this account: he likens them to wolves in sheep's clothing.
CCC 2286: Scandal can be provoked by laws or institutions, by fashion or opinion. Therefore, they are guilty of scandal who establish laws or social structures leading to the decline of morals and the corruption of religious practice.
CCC 2287: Anyone who uses the power at his disposal in such a way that it leads others to do wrong becomes guilty of scandal and responsible for the evil that he has directly or indirectly encouraged. "Temptations to sin are sure to come; but woe to him by whom they come!"
Meanwhile, the same Catechism also uses the word scandal in this way:
CCC 588: Jesus scandalized the Pharisees by eating with tax collectors and sinners as familiarly as with themselves.
CCC 589: Jesus gave scandal above all when he identified his merciful conduct toward sinners with God's own attitude toward them.
CCC 1336: The first announcement of the Eucharist divided the disciples, just as the announcement of the Passion scandalized them.
We should recognize instinctively that these two meanings of scandal cannot be same, for we know that Jesus never sinned. He never led anyone to do evil, He never became His neighbor’s tempter, and He never drew anyone into spiritual death. This would be a patently absurd premise for any Christian to defend.
Instead, we can make an distinction, such as Cardinal Burke articulated in 2007:
Here, it is necessary to note two meanings of the term, scandal, in Church discipline. The first and properly theological meaning of scandal is to do or omit something which leads others into error or sin. The second meaning is to do or omit something which causes wonderment (admiratio) in others.
Thus the first (proper) sense of scandal – leading our neighbor to do evil – is inherently sinful. But the second (equivocal) sense of scandal – causing our neighbor to wonder, or be concerned, or be shocked and surprised – is not necessarily linked to any sin, although of course it can be.
Wonderment can arise from something materially sinful. This is what happens when a sinful action or behavior is encouraged. If we encourage something sinful (either explicitly or implicitly) then we are by definition leading our neighbor into sin.
Note: In principle, sin should cause wonderment and concern. Lack of concern over sin (especially grave sin) is never good, and can even be a clear sign of moral degradation. If grave sin does not provoke wonderment-scandal in a community, then the moral compass of the community needs reform.
Wonderment can arise from something materially good or justifiable. This is the form of “scandal” that Jesus gave through his public ministry, which was never materially sinful. When we model or encourage non-sinful behaviors to our neighbor, we are not leading them into any sin, no matter how shocked they might be.
Note: If morally good things are causing shock or “scandal” in the community, this is also a sign that the moral compass of the community needs reform.

Thomas Aquinas makes a more complex distinction – regarding “active scandal” and “passive scandal” – in Summa Theologiae II.2, Q.43: A.1, Reply to Objection 4:
Another's words or deed may be the cause of another's sin in two ways, directly and accidentally. Directly, when a man either intends [to] lead another man into sin, or, if he does not so intend, when his deed is of such a nature as to lead another into sin: for instance, when a man publicly commits a sin or does something that has an appearance of sin. On this case… properly speaking, [he affords] an occasion of another's spiritual downfall, wherefore his act is called "active scandal."
One man's word or deed is the accidental cause of another's sin, when he neither intends to lead him into sin, nor does [anything] of a nature to lead him into sin, and yet this other [person], through being ill-disposed, is led into sin… [in this case] he who does this righteous act, does not [give] an occasion of the other's downfall, but it is [the other person] who takes the occasion… this is "passive [scandal]" without "active scandal," since he that acts rightly does not, for his own part, afford the occasion of the other's downfall.
Saying this again, more simply:
“Active scandal” is giving or offering a direct occasion for sin.
“Passive scandal” is taking or receiving an occasion for sin – either a direct occasion (that was being offered), or an accidental (if it was not being offered).
And a critical key lies in understanding the ways these things can exist:
Sometimes there is active scandal in one person, together with passive scandal in another person: such as when one is encouraged to sin and consents.
Sometimes there is active scandal in one person, without any passive scandal in another person: such as when one is encouraged to sin but does not consent.
Sometimes there is no active scandal, but only passive scandal in one person: such as when one acts rightly yet another still “takes” the occasion to sin.
Alternatively, this third option can be reformulated in a more technical manner that Aquinas proposes: for we might insist that passive scandal must always be due to some active scandal – yet “this active scandal is not always in another person, but in the very person who is scandalized, because, to wit, he scandalizes himself.” (Summa Theologiae II.2, Q.43: A.6, Reply to Objection 1).
Thus those who (like the Pharisees) are provoked to wonderment by a morally good action, and insist on “taking” scandal even after being given an explanation about why an action is morally permissible – or worse, insist on stirring up “scandal” in the community – such persons are not being “given” scandal by any external source, but are only scandalizing themselves. This sub-type of scandal is termed “pharisaic scandal”, and on this Aquinas notes further (Summa Theologiae II.2, Q.43: A.7, Response):
[Scandal] sometimes proceeds from malice, for instance when a man wishes to hinder [certain] spiritual goods by stirring up scandal. This is the "scandal of the Pharisees," who were scandalized at Our Lord's teaching: and Our Lord teaches (Matthew 15:14) that we ought to treat such like scandal with contempt.

But there is also another sub-type of scandal, termed “scandal of the weak”, which is traditionally drawn from the text of 1 Corinthians 8: 9-13 (RSVCE):
Be careful, however, that the exercise of your rights does not become a stumbling block to the weak. For if someone with a weak conscience sees you, with all your knowledge, eating in an idol’s temple, won’t that person be emboldened to eat what is sacrificed to idols? So this weak brother or sister, for whom Christ died, is destroyed by your knowledge. When you sin against them in this way and wound their weak conscience, you sin against Christ. Therefore, if what I eat causes my brother or sister to fall into sin, I will never eat meat again, so that I will not cause them to fall.
And on this, Aquinas also writes (Summa Theologiae II.2, Q.43: A.7, Response):
Sometimes scandal proceeds from weakness or ignorance, and such is the "scandal of little ones." In order to avoid this kind of scandal, spiritual goods ought to be either concealed, or sometimes even deferred (if this can be done without incurring immediate danger), until the matter being explained the scandal cease. If, however, the scandal continue after the matter has been explained, it would seem to be due to malice, and then it would no longer be right to forego that spiritual good in order to avoid such like scandal.
Thus, even though we do have a real moral obligation (in charity) to avoid giving this sort of scandal to our neighbor, this obligation to our neighbor can be fulfilled in at least three ways: (1) by concealing or reducing the visibility of the non-sinful action; or (2) by deferring or refraining from the non-sinful action; and finally (3) by offering an appropriate explanation to them about why the matter is not sinful.
Of course, judging which option is best in a given set of circumstances requires prayerful discernment and prudence, but the point is this: the appearance of sin and any danger of accidentally leading another into sin through a morally good or objectively non-sinful action is naturally mitigated through appropriate transparency, education, and clarification whenever concerns are raised. Those who insist on rejecting truthful explanations are ultimately responsible for themselves.
And indeed, not is every stumbling block [Greek: σκάνδαλον, skandalon] is a bad thing. Some stumbling blocks are not invitations to sin, but simple opportunities for growth, in which the only thing we truly stumble against is ourselves – our own false beliefs and preconceptions – after being confronted by something true. This is the sense in which we refer to the scandal of the cross as something good, in resonance with Saint Paul’s observation that “we preach Christ crucified, a stumbling block [σκάνδαλον, skandalon] to Jews and folly to Gentiles” (1 Corinthians 1:23, RSVCE).
Summarizing up to this point, we can articulate two guiding principles:
Whenever materially sinful behavior is present, concern about scandal in the strict and proper theological sense (active scandal) is always real – especially if we are dealing with materially grave sin. For even if no one in the community is passively “taking” scandal, that sinful error or behavior is still being actively “offered”, and thus at least the danger of leading someone into sin is always necessarily present.
But whenever a behavior involves no material sin, concern about active scandal is not theologically defensible. When nothing sinful is actually being “offered” to the community, cries and accusations of scandal are fundamentally wrong.
Sincere concerns, however, should receive an appropriate explanation about why this behavior is not sinful, along with a reminder that we should always prefer to extend the more charitable interpretation to our neighbor, and avoid rushing to judgment:
CCC 2478: To avoid rash judgment, everyone should be careful to interpret insofar as possible his neighbor's thoughts, words, and deeds in a favorable way:
Every good Christian ought to be more ready to give a favorable interpretation to another's statement than to condemn it. But if he cannot do so, let him ask how the other understands it. And if the latter understands it badly, let the former correct him with love. If that does not suffice, let the Christian try all suitable ways to bring the other to a correct interpretation so that he may be saved. [St. Ignatius of Loyola]
Finally, another useful (and very rigorous) framework for analyzing scandal can be drawn from Dominic Prümmer’s Handbook of Moral Theology (nn. 230-232).
Dominic M. Prümmer, O.P., (1866–1931) was a Dominican priest, canon lawyer, and theology professor at the University of Fribourg.
For the remainder of this entry, I will be presenting the 1956 English translation of Prümmer’s text in a slightly reorganized format, with minimal alterations to the original terminology.
n. 230 – Definitions and Kinds:
Scandal is some word or deed (whether of omission or commission) that is itself evil or has the appearance of evil and provides an occasion of sin to another.
Active scandal is the act itself which is the occasion of sin for another.
Active scandal is direct if the sin of another is intended.
Direct scandal is diabolical or formal if through hatred of God or neighbor the sin of another is intended precisely as sin.
Direct scandal is simply direct when the neighbor's sin is intended for some other purpose, such as pleasure or revenge, etc.
Active scandal is indirect if the sin is not intended but is foreseen.
Passive scandal is the sin occasioned by another's act.
Passive scandal is given when it is produced by the evil action of another.
Passive scandal is taken when it results not from an evil action but from a good action which is accepted by another either through ignorance (scandal of the weak) or through malice (pharisaic scandal) as an occasion of sin.
n. 231 – The Sinfulness of Scandal:
Direct scandal is a mortal sin, both against charity and against that virtue which the neighbor is encouraged to violate, but it admits of slight matter. Direct scandal is a venial sin if the act is imperfect or if the matter is slight.
Indirect scandal is a sin, probably against charity only. Since in indirect scandal the violation of a virtue by the person taking scandal is foreseen but not desired, it is more probable that the sin is contrary to charity only, and not [also] to the virtue whose violation is not desired. There are some, however, who maintain the contrary view.
The gravity of the sinfulness of scandal increases: (a) the more one desires the sin of another; (b) the greater the influence which the action exercises on the sin of another; (c) the more serious the sin committed by the neighbor.
On the other hand the gravity of the sin decreases: (a) the less perfect the deliberation; (b) the less influence exerted by the action on the sin of another; (c) the less serious the sin which the neighbor is induced to commit.
n. 232 – The Obligation of Avoiding Scandal:
There is no obligation to avoid pharisaic scandal, provided there is some reasonable cause for the action causing it. This follows from the fact that pharisaic scandal is caused by the malice of the person taking scandal.
Scandal of the weak must be avoided, if this can be done without grave inconvenience. Charity demands that we prevent an innocent neighbor suffering harm, so far as this is morally possible.
For a just cause it is lawful to permit and even to provide the occasion of another's sin. In such circumstances the neighbor's sin is not intended, and even God himself permits the occasions of sin.
Reparation for scandal given is necessary since it is frequently an offense against the public good and not merely against charity. Commutative justice is also affected if the neighbor is induced to sin by threats, force, deceit, etc. Reparation is made either publicly or secretly in accord with the scandal being public or secret.
Thanks for another good post, Daniel. I'm working on publishing something shortly which is going to walk some lines around this.