Ockham gives a proof that we have a single concept said of all things, while also claiming that it is not “being”.
First, the proof:
1.) If there is not one concept common to all, there are many common to some. them be A and B.
2.) Let A and B be said of something (aliquid) C.
3.) We can thus make three claims “C is A”, “C is B” and “C is something (aliquid)”. Ex hypothesi, the first two are different, and the third is different from both, for it is certain while the first two are uncertain.
4.) The third claim cannot be less universal than either of the first two, and it could be convertible in universality with at most one of them, therefore “something” is in fact more universal than both.
5.) Therefore, “something” is a single concept common to all.
But Ockham immediately adds
tamen hoc nomen “ens” est aequivocum quia non preadicatur de omnibus subiicibilibus, quando significative sumuntur secundum unam conceptum, sed diversi sibi conceptus correspondent.
But this name (word? noun?) “being” is equivocal, because it is not predicated of whatever-can-be-a- subject as one concept when it is taken to signify: rather, diverse concepts correspond to it.
Seen in this way, the Thomist-Ockamist dispute about the univocity of being seems to come to this: if St. Thomas looked at Ockham’s “something” proof he’d say “if logic tells you about some unified field beyond being, then this unified field is an illusion that philosophy should dispel. Your logic should be subordinate to the natures of things, and gets its truth from the presence of reality within it. All you’ve done is prove the existence of some positive logical being with no real being corresponding to it. Throw it away or mark it off as some sort of no-man’s land”
But perhaps it’s not that simple. This “aliquid” might map pretty well over St. Thomas’s idea of being as true , where “true” is understood as the composition of a predicate with whatever can be a subject. Doesn’t STA insist that the existence of God can only be proven if we take “existence” in the mode of being as true?
“To be” can mean either of two things. It may mean the act of essence, or it may mean the composition of a proposition effected by the mind in joining a predicate to a subject. Taking “to be” in the first sense, we cannot understand God’s existence nor His essence; but only in the second sense.
ST 1.3.4 ad.2 ital. mine.