Matter is something common which is found in all things;[352]
nevertheless it does not form a genus because it does not admit of any
differences, unless its differences consist in appearing in different
forms; as, here, fire, and there, air. Philosophers who consider that
matter is a genus base this opinion on the fact that matter is common
to all the things in which it exists, or that it stands in the relation
of the whole to the parts of particular objects (or, "matters"). In
this case, however, the term "genus" would be used in a sense differing
from the one it bears usually. It would then be no more than an only
or single element, if we admit that an element can be a genus. If,
conceiving that matter is united to matter, or exists within it, we add
form to matter, matter would thereby be differentiated from the other
forms, but it will not comprehend every being-like form. Were we to
call the generating principle of being "form," and were we to call the
reason which constitutes the form "being-like reason," we shall not
yet have clearly defined the nature of "being." Finally, if we give the
name of "being" only to the combination of matter and form, the result
will be that neither of these two (matter or form taken separately)
will themselves be "being." If, however, we were to assert that not
only their combination, but also each of them separately were "being,"
we then would be faced with the problem of what is common to all three.