e is potentiality to
blackness, is the whole substance of the white thing; since whiteness
is not a part thereof; whereas the subject of the form of air is part
thereof: hence when it is said, "Air can be fire," it is verified by
synecdoche by reason of the part. But in this conversion, and
similarly in creation, because there is no subject, it is not said
that one extreme can be the other, as that "non-being can be being,"
or that "bread can be the body of Christ": and for the same reason it
cannot be properly said that "being is made of (_de_) non-being," or
that "the body of Christ is made of bread," because this preposition
"of" (_de_) denotes a consubstantial cause, which consubstantiality
of the extremes in natural transmutations is considered according to
something common in the subject. And for the same reason it is not
granted that "bread will be the body of Christ," or that it "may
become the body of Christ," just as it is not granted in creation
that "non-being will be being," or that "non-being may become being,"
because this manner of speaking is verified in natural transmutations
by reason of the subject: for instance, when we say that "a white
thing becomes black," or "a white thing will be black."

Nevertheless, since in this sacrament, after the change, something
remains the same, namely, the accidents of the bread, as stated above
(A. 5), some of these expressions may be admitted by way of
similitude, namely, that "bread is the body of Christ," or, "bread
will be the body of Christ," or "the body of Christ is made of
bread"; provided that by the word "bread" is not understood the
substance of bread, but in general "that which is contained under the
species of bread," under which species there is first contained the
substance of bread, and afterwards the body of Christ.

Reply Obj. 1: That out of which something else is made, sometimes
implies together with the subject, one of the extremes of the
transmutation, as when it is said "a black thing is made out of a
white one"; but sometimes it implies only the opposite or the
extreme, as when it is said--"out of morning comes the day." And so
it is not granted that the latter becomes the former, that is, "that
morning becomes the day." So likewise in the matter in hand, although
it may be said properly that "the body of Christ is made out of
bread," yet it is not said properly that "bread becomes the body of
Christ," except by similitude, as was said abov