; the contrary of which appears in
every natural transmutation.

Again, this conversion has something in common with natural
transmutation in two respects, although not in the same fashion.
First of all because in both, one of the extremes passes into the
other, as bread into Christ's body, and air into fire; whereas
non-being is not converted into being. But this comes to pass
differently on the one side and on the other; for in this sacrament
the whole substance of the bread passes into the whole body of
Christ; whereas in natural transmutation the matter of the one
receives the form of the other, the previous form being laid aside.
Secondly, they have this in common, that on both sides something
remains the same; whereas this does not happen in creation: yet
differently; for the same matter or subject remains in natural
transmutation; whereas in this sacrament the same accidents remain.

From these observations we can gather the various ways of speaking in
such matters. For, because in no one of the aforesaid three things
are the extremes coexistent, therefore in none of them can one
extreme be predicated of the other by the substantive verb of the
present tense: for we do not say, "Non-being is being" or, "Bread is
the body of Christ," or, "Air is fire," or, "White is black." Yet
because of the relationship of the extremes in all of them we can use
the preposition _ex_ (out of), which denotes order; for we can truly
and properly say that "being is made out of non-being," and "out of
bread, the body of Christ," and "out of air, fire," and "out of
white, black." But because in creation one of the extremes does not
pass into the other, we cannot use the word "conversion" in creation,
so as to say that "non-being is converted into being": we can,
however, use the word in this sacrament, just as in natural
transmutation. But since in this sacrament the whole substance is
converted into the whole substance, on that account this conversion
is properly termed transubstantiation.

Again, since there is no subject of this conversion, the things which
are true in natural conversion by reason of the subject, are not to
be granted in this conversion. And in the first place indeed it is
evident that potentiality to the opposite follows a subject, by
reason whereof we say that "a white thing can be black," or that "air
can be fire"; although the latter is not so proper as the former: for
the subject of whiteness, in which ther