Hume vs. Aquinas on Transubstantiation

Benedict Ashley, O.P., in his book The Way toward Wisdom (p. 511 n. 53), cites Hume's claim, which he borrowed from Dr. Tillotson, that the transubstantiation, "since it denies the evidence of the senses on which all certitude rests," "leads to skepticism:"

I flatter myself, that I have discovered an argument of a like nature, which, if just, will, with the wise and learned, be an everlasting check to all kinds of superstitious delusion, and consequently, will be useful as long as the world endures.

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Suppose, for instance, that the fact, which the testimony endeavours to establish, partakes of the extraordinary and the marvellous; in that case, the evidence, resulting from the testimony, admits of a diminution, greater or less, in proportion as the fact is more or less unusual. The reason why we place any credit in witnesses and historians, is not derived from any connexion, which we perceive a priori, between testimony and reality, but because we are accustomed to find a conformity between them. But when the fact attested is such a one as has seldom fallen under our observation, here is a contest of two opposite experiences; of which the one destroys the other, as far as its force goes, and the superior can only operate on the mind by the force, which remains.

—David Hume's Enquiry of Human Understanding, sec. 10 "On Miracles" part 1

Benedict Ashley, O.P., responds:

Yet we experience that very unusual events do in fact occur! Why must we, then, always doubt the testimony of others about such events? Sense experiences are signs to be intellectually interpreted always in their contexts. The proper accidents of bread and wine naturally signify these substances, but for the Catholic faith the context of the Eucharist established by God permits the appearance of bread and wine to signify without deception [Summa Theologiæ, IIIª q. 75 a. 5 arg. 2 et ad 2] Christ's body and blood. Although this is not strictly a "miracle" (since the change is not evident to our senses and hence is extremely improbable as regard natural reason), as Aquinas shows [Summa Theologiæ, IIIª q. 75 a. 5 arg. 3 et ad 3], it is not impossible; and if the Catholic faith is credible, as apologetic seeks to show, reason demands that it be believed on the testimony of the Church. Similarly, the context of the Bible as read in the tradition of the Church (which one would suppose Tillotson accepted) permits it to signify the mind of God, not merely the intent of its human authors. Hume's argument amount to declaring that he is determined to interpret his experiences a way that will not disturb his "common sense" habits; but life is full of uncomfortable events.

The above-mentioned St. Thomas Aquinas Summa Theologiæ quotes are:

Objection 2. Further, there ought not to be any deception in a sacrament of truth. But we judge of substance by accidents. It seems, then, that human judgment is deceived, if, while the accidents remain, the substance of the bread does not. Consequently this is unbecoming to this sacrament.

Objection 3. Further, although our faith is not subject to reason, still it is not contrary to reason, but above it, as was said in the beginning of this work (Summa Theologiæ, Iª q. 1 a. 6 ad 2 et a. 8). But our reason has its origin in the senses. Therefore our faith ought not to be contrary to the senses, as it is when sense judges that to be bread which faith believes to be the substance of Christ's body. Therefore it is not befitting this sacrament for the accidents of bread to remain subject to the senses, and for the substance of bread not to remain.

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Reply to Objection 2 and 3. There is no deception in this sacrament; for the accidents which are discerned by the senses are truly present. But the intellect, whose proper object is substance as is said in De Anima iii, is preserved by faith from deception. And this serves as answer to the third argument; because faith is not contrary to the senses, but concerns things to which sense does not reach.