Anthony Kenny, echoing Peter Geach, argues that it is absurd to say that God’s essence is the same as his existence since this would mean that the answer to “what is God” would be “there is one”. Can we reconstruct a Thomistic response to this?
First, translating the Kenny/Geach objection into Thomistic language gives us something like this: the questions “whether it is” and “what it is” are irreducible, and thus the one can never serve to answer the other. St. Thomas was aware that these questions were irreducible and yet he still posits at least one “what” question (sc. about the divine essence) which terminates in a “whether” answer (that it is “esse”).
St. Thomas articulates the problem very close to this in QDP 7.2, arg. 2.
The two questions whether it is and what it is are diverse, and we know how to respond to one of these and not to the other, as is clear from the authority cited above (Damascene -ed.) So what corresponds to the “whether it is” of God and the “what it is” is not the same, but the first corresponds to existence and the second to substance or nature.
duae quaestiones diversae sunt, an est, et quid est; ad quarum unam respondere scimus, ad aliam vero non, ut etiam ex praedicta auctoritate patet. Ergo id quod respondet ad an est de Deo, et quod respondet ad quid est, non est idem; sed ad an est respondet esse; ad quid est, substantia vel natura.
Problematically, STA rolls this objection in with two others and then gives a reply that he gives other places:
Being and existence are said in two ways, as Metaphysics V makes clear. Sometimes they signify the essence of a thing or the act of being, sometimes they signify the truth of a proposition, even in things that do not exist; as when we say that “blindness exists” because it is true that a man is blind. So when Damascene says that the existence of God is shown to us, the existence of God is taken in the second way and not in the first. For in the first way the existence of God is the same as what his substance is; and as his substance is unknown, so is his existence. But we do understand in the second way that God is, since we conceive this proposition in our intellect from his effects.
ens et esse dicitur dupliciter, ut patet V Metaph. Quandoque enim significat essentiam rei, sive actum essendi; quandoque vero significat veritatem propositionis, etiam in his quae esse non habent: sicut dicimus quod caecitas est, quia verum est hominem esse caecum. Cum ergo dicat Damascenus, quod esse Dei est nobis manifestum, accipitur esse Dei secundo modo, et non primo. Primo enim modo est idem esse Dei quod est substantia: et sicut eius substantia est ignota, ita et esse. Secundo autem modo scimus quoniam Deus est, quoniam hanc propositionem in intellectu nostro concipimus ex effectibus ipsius.
Cajetan fleshes out this response, albeit while addressing a slightly different question:
The existence of God differs from the rest of beings in this, that the existence of God is the “what it is” of God himself, such that this proposition “God is” is said in the first way of speaking per se. The existence of the rest of things does not stand to them in this way, but is distinguished from their nature. From this it arises that the existence of God, in itself and absolutely, is the proper terminus of the question “what it is”, and it is the foundation of the question “whether it is” only relatively (secundum quid) i.e. so far as it grounds the truth of a proposition. The existence of other beings is not put in view from the question “what it is” because it is not predicated of them according to the first mode of speaking per se, as is clear inductively (“man is”, “the sky is”, etc.) but it is put into view simply and in itself by the question “whether it is”. And because of this, when we know about other things the answer to the question “whether it is” we are said to know both the existence that is the truth of the proposition and the very existence of the thing (STA’s two modes of being mentioned above – ed.) because the thing is known in the proper way in which it is knowable. But when we know the answer to the question “whether it is” about God, we are said to know it according to the truth of the proposition and not the very existence of God – not because the ultimate term of our knowledge is the existence of a proposition… but because by this knowledge the existence of God is not known as it is knowable in itself by the appropriate question, since it is not known through the nature (quid) of God.
Notice how Cajetan answer rests on the modes of perseity, where God is said to exist per se in the first sense while nothing else does. This is the mode where a predicate is said of something because it belongs to it intrinsically and by its nature, the way we say fire is hot or elephants are placental mammals (by way of contrast, a stone is not hot per se, nor is an elephant angry or a father per se). Roughly, what being a placental mammal is to a antelope, existence is to God. We are, however, incapable of seeing the truth of the comparison by knowing what God is in himself. Here is it important to divide the theoretical knowledge we can have of sensible or physical things from the knowledge we can have of God. Though we know some natural things by their effects (say, an undiscovered planet) this does not preclude us knowing the planet in itself (say, by seeing it in a telescope, or sending astronauts on the long journey to see it). God is not knowable in this way, but only through his effects. To put it in Franciscan/ Kantian terms, natural things are always in principle given in intuition to us while God is not. Taken in this sense, the basic Thomistic claim is that there need not be an intuition for every object known, but only of those whose existence is different from essence.
If this is the right line of critique, then a response to the Kenny/Geach objection pushes us to see at least three things: a.) the modes of perseity, b.) the unknowability of God’s esse in itself, which can be known from the esse that is the truth of a proposition and c.) the differing modes of knowing intuitive and non-intuitive beings.