Thomas Aquinas, the “angelic doctor,” in his _Summa Theologiæ_ raises the query, whether it is permissible to curse irrational creatures (_utrum liceat irrationabiles creaturas adjurare_). He states, in the first place, that curses and blessings can be pronounced only upon such things as are susceptible of receiving evil or good impressions from them, or in other words, upon sentient and rational beings, or upon irrational creatures and insentient things in their relation to rational beings, so that the latter are the objects ultimately aimed at and favourably or unfavourably affected. Thus God cursed the earth, because it is essential to a man’s subsistence; Jesus cursed the barren fig-tree symbolizing the Jews, who made a great show of leafage in the form of rites and ceremonies, but bore no fruits of righteousness; Job cursed the day on which he was born, because he took from his mother’s womb the taint of original sin; David cursed the rocks and mountains of Gilboa, because they were stained with the blood of “the beauty of Israel”; in like manner the Lord sends locusts and blight and mildew to destroy the harvests, because these are intimately connected with the happiness of mankind, whose sins he wishes to punish.
It is laid down as a legal maxim by mediæval jurisprudents that no animal devoid of understanding can commit a fault (_nec enim potest animal injuriam fecisse quod sensu caret_). This doctrine is endorsed by the great theologian and scholastic Thomas of Aquino. If we regard the lower animals, he says, as creatures coming from the hand of God and employed by him as agents for the execution of his judgments, then to curse them would be blasphemous; if, on the other hand, we curse them _secundem se_, i.e. merely as brute beasts, then the malediction is odious and vain and therefore unlawful (_est odiosum et vanum et per consequens illicitum_). There is, however, another ground, on which the right of excommunication or anathematization may be asserted and fully vindicated, namely, that the lower animals are satellites of Satan “instigated by the powers of hell and therefore proper to be cursed,” as the Doctor angelicus puts it. Chassenée refers to this opinion in the treatise already cited (I. § 75), and adds “the anathema then is not to be pronounced against the animals as such, but should be hurled inferentially (_per modum conclusionis_) at the devil, who makes use of irrational creatures to our detriment.” This notion seems to have been generally accepted in the Middle Ages, and the fact that evil spirits are often mentioned in the Bible metaphorically or symbolically as animals and assumed to be incarnate in the adder, the asp, the basilisk, the dragon, the lion, the leviathan, the serpent, the scorpion, etc., was considered confirmatory of this view.