hing common to all, is an
addition to it. But "being" is divided by "one" and by "many."
Therefore "one" is an addition to "being."

Obj. 3: Further, if "one" is not an addition to "being," "one"
and "being" must have the same meaning. But it would be nugatory to
call "being" by the name of "being"; therefore it would be equally so
to call being "one." Now this is false. Therefore "one" is an addition
to "being."

_On the contrary,_ Dionysius says (Div. Nom. 5, ult.): "Nothing which
exists is not in some way one," which would be false if "one" were an
addition to "being," in the sense of limiting it. Therefore "one" is
not an addition to "being."

_I answer that,_ "One" does not add any reality to "being"; but is only
a negation of division; for "one" means undivided "being." This is the
very reason why "one" is the same as "being." Now every being is
either simple or compound. But what is simple is undivided, both
actually and potentially. Whereas what is compound, has not being
whilst its parts are divided, but after they make up and compose it.
Hence it is manifest that the being of anything consists in
undivision; and hence it is that everything guards its unity as it
guards its being.

Reply Obj. 1: Some, thinking that the "one" convertible with "being"
is the same as the "one" which is the principle of number, were
divided into contrary opinions. Pythagoras and Plato, seeing that the
"one" convertible with "being" did not add any reality to "being,"
but signified the substance of "being" as undivided, thought that the
same applied to the "one" which is the principle of number. And
because number is composed of unities, they thought that numbers were
the substances of all things. Avicenna, however, on the contrary,
considering that "one" which is the principle of number, added a
reality to the substance of "being" (otherwise number made of unities
would not be a species of quantity), thought that the "one"
convertible with "being" added a reality to the substance of beings;
as "white" to "man." This, however, is manifestly false, inasmuch as
each thing is "one" by its substance. For if a thing were "one" by
anything else but by its substance, since this again would be "one,"
supposing it were again "one" by another thing, we should be driven
on to infinity. Hence we must adhere to the former statement;
therefore we must say that the "one" which is convertible with
"being," does not add a reality to being; but