According to St. Thomas (II-II:43:1) 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
