1. Just as the formal reason for hypostasis is "to be through itself," or, "to subsist through itself," so the formal reason for substance is "to be in itself" and "actually not to be sustained in another as the first subject"; for, rightly are those two to be distinguished: "to be through itself" (which is the formal reason for hypostasis), and "to be in itself" (which is the formal reason for substance).
2. Therefore, just as human nature in Christ is not hypostasis, because it does not subsist through itself but is assumed from a superior divine hypostasis, so finite substance, for example, the substance of bread, ceases to be substance by this alone and without any change of itself, because it is sustained supernaturally in another, so that it is not already in itself, but in another as in a first subject.
3. Thus, transubstantiation, or the conversion of the entire substance of bread into the substance of the body of Christ our Lord, can be explained in this way, that the body of Christ, while it becomes substantially present in the Eucharist, sustains the nature of bread, which by this very fact and without any change in itself ceases to be substance, because it is not now in itself, but in another sustaining; and, indeed, the nature of bread remains, but in it the formal reason for substance ceases; and so there are not two substances, but one only, that, of course, of the body of Christ.
4. Therefore, in the Eucharist the matter and form of the elements of bread remain; but now, existing supernaturally in another, they do not have the nature of substance, but they have the nature of supernatural accident, not as if in the manner of natural accidents they affected the body of Christ, but on this account, insofar as they are sustained by the body of Christ in the manner in which it has been said."
