The logic of existence

It is not impossible to reconstruct a response from Thomas to the dilemma posed at the end of the last chapter, and it is obviously important that we should find some way of doing so, because the dilemma strikes at the heart of my argument in this essay. For if logic required a choice between the rational demonstrability of the existence of God, but at the price of abandoning a theological apophaticism, and holding on to the apophaticism, but at the price of abandoning the rational demon-strability of God - then it would seem that my argument would fail just as its critics say it must: the existence of God is rationally demonstrable on pain of onto-theological error - in short, of idolatry. But I shall argue in this chapter that the case for maintaining both propositions does not yet have to be abandoned, and that Thomas is not without resources to repel the 'Derridean' counter-argument. And we may begin by noting that Thomas himself entertains an objection similar in form to Derrida's, albeit to a different, if closely related issue.

The objection arises in connection with Thomas's doctrine of the divine simplicity, and more particularly with the proposition that definitive of that simplicity is the identity of God's esse and essentia. It would seem, Thomas says, that since we can know whether God exists (an Deus sit) but not what God is (quid sit Deus) esse and essentia can no more be identical in God than they are in anything else. The objection is doubly significant in its bearing on our discussion, for, in the first place, in posing this objection Thomas is explicitly screwing up the tension between his theological apophaticism and his case for the rational demonstrability of God's existence. For if by demonstration we can know God to exist, then how can it be the case also that we do not know the divine esse? Put in the starkest possible terms, Thomas's position seems to be straightforwardly self-contradictory in that it seems to amount to saying that we can know God's existence, but also that we cannot. He cannot have it both ways. If God's existence is unknown to us in principle, then no proof can make it known to us. And if a proof can make God's existence known to us, then God's existence is not unknown to us.

But this objection is significant for a second reason, which brings us back to our earlier discussion of Scotus. For the principle underlying it is just that which Scotus employed in his argument that esse is predicated univocally of God and of creatures. For if, Scotus argued, we can know that p while not knowing whether or not that q, then p and q must be really distinct. Hence, if we can know that God is 'being' (ens), but be so ignorant as not yet to know whether God is infinite or finite being, then esse must be predicable in some one sense independently of the distinction between infinite and finite, and so univocally of both God and creatures. Consequently, as Cross comments,1 what gives way in Scotus' case is the apophaticism, which yields inevitably to his principal concern, which is for the rational demonstrability of God's existence. As we shall see, Thomas feels uncompelled by the force of this dilemma to abandon either the apophaticism or the rational demonstrability of God, and his reply to the objection is to make a distinction and to note how

Esse can be understood in two ways. In the first sense it means 'the act of existing' (actus essendi); in the second it refers to the formation of [an affirmative] proposition which the mind constructs by means of a predicative form. Hence, in the first sense of esse, we cannot know the esse of God any more than we can know his essence, but only in the second sense. For we know that the proposition which we construct about God when we say 'God exists' is true. And we know this from his effects, as we showed in q2 a2.2

Let us say, for the purposes of exposition, that the first manner of understanding esse is as expressed in judgements of 'actuality', and the second is as expressed in affirmative predicative propositions, and note, as a first step of explanation, that we cannot get at the distinction in the logical form Thomas here has in mind by means of any purely grammatical devices. For the one statement 'x exists' can be a proposition of either logical form, regardless of what value we substitute for the variable 'x'. Moreover, we ought not to allow this terminology, descriptive of the second sort of proposition as 'predicative', to mislead us into supposing that, for Thomas, esse in this sense is logically a predicate, for it is not. As we shall see, what Thomas appears to mean by the ascription of esse in

2 'Esse dupliciter dicitur: uno modo, significat actum essendi; alio modo, significat compo-sitionem propositionis, quam anima adinvenit coniungens praedicatum subiecto. Primo igitur modo accipiendo esse, non possumus scire esse Dei, sicut nec eius essentiam: sed solum secundo modo. Scimus enim quod haec propositio quam formamus de Deo, cum dicimus Deus est, vera est. Et hoc scimus ex eius effectibus, ut supra [q2 a2] dictum est.' ST 1a q3 a4 ad2.

this second sense is not that esse is predicable of the variable 'x', but that any such statement of existence - 'God exists', or for that matter, 'cows exist' - may be replaced by some affirmative statement in which 'God' and 'cow' form predicates of something or other: 'something or other is God'; 'something or other is a cow'. To put it in the terms of modern logic, the 'exists' in predications of this kind is analysable in terms of the 'existential quantifier'.

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