[margin: Cajetan, in the Summa, under “superstition.”]
I shall speak briefly. First, if it is established that the effect exceeds the powers of nature, then it is necessary to consider whether, by sacred Scripture, by a definition of the Church, or by a tradition approved by the Church, that effect is attributed to God; or, what is the same thing, whether it is established by testimony of this kind that this effect is divine. If nothing of this kind is found, the effect must be attributed to a pact entered into with a demon, and therefore it must be judged a magical superstition, at least of vain observance.
Effects of this kind are remission of sins outside the sacraments, as regards mortal sins; outside the sacramentals, as regards venial faults; likewise divination of future contingent things; and the bending or directing of those actions which depend merely on the freedom of the will.
Second, if it is established that the thing to which the effect is attributed has this power from God or from nature, there is not vain observance on the side of the effect. Yet there could be vain observance by reason of some faulty circumstance. For example, a hairshirt, discipline, and fasting, because they afflict and mortify the body, are endowed with power to restrain carnal concupiscences springing from the powers of the flesh and from an excessively flourishing bodily habit. But if you add to these things ridiculous circumstances not ordained for this purpose by nature, God, or the Church, such as a fixed hour, a defined number which one may neither exceed nor diminish, the presence of certain persons, or that it be done with this or that hand, with a silk scourge, and things of this sort, it will be vain observance. From these rules it follows that the following things are vain observance.