What is the analogy of being?

Thomas Aquinas, answered from the texts and cited to the page.

Thomas Aquinas answers

Univocal predication of God and creatures is impossible, and pure equivocation is equally ruinous — for if the term shifts sense entirely between premises and conclusion, no reasoning from creatures to God holds at all, and the Apostle's word that the invisible things of God are clearly seen through the things that are made would be empty.¹

The resolution is analogy, that is, predication according to proportion. Consider how "healthy" is said of an animal, of medicine, and of urine: not in one flat sense, nor in three unrelated senses, but because medicine causes health in the animal and urine signifies it, so that the one thing — animal health — orders all three uses.² The same term carries different but related meanings, and the relation is what saves the inference.

Now there are two modes of this analogical community.³ In the first, several things are referred to some one third thing, as medicine, food, and urine are all referred to the health of the body. In the second, two things are ordered to one another directly, without a third term — as being is said of substance and accident, because accident has a relation to substance, not because both are referred to something prior.⁴

It is in this second mode that names are predicated of God and creatures; the first mode would require positing something prior to God, which is impossible.⁵ There is a further distinction I draw in the disputed questions on truth, between analogy of proportion and analogy of proportionality.⁶ In proportion, one thing has a determinate relation to another, as two has to unity.

In proportionality, what is shared is a similarity of relations: as six is to three, so four is to two. Now nothing can be predicated of God and creature by the first mode of analogy, because no creature stands in a determinate, measurable relation to God such that the divine perfection could be fixed by it. But in proportionality there is no such definite distance required, and so a name may travel from creature to God along the likeness of relations without claiming to measure what God is.⁷

What this means for the name "wise," said of a man and of God, is worth stating plainly. Said of a man, "wise" signifies a perfection distinct from his essence, from his power, from his existence — it circumscribes something in him.⁸ Said of God, the same term leaves the thing signified incomprehended, exceeding the signification of the name, because in God wisdom is not distinct from essence or existence or power.⁹

The term is not the same in sense; neither is it wholly other. It travels along the relation of creaturely perfection to its source, in whom all such perfections pre-exist unitedly and without division.¹⁰ The likeness of the creature to God is real but imperfect, for it does not represent one and the same generic thing.¹¹ God is not a being among beings, a member of a genus that includes both him and us.

He is the cause of the whole species, and such a cause is not univocal with its effects — yet neither is it equivocal, for otherwise it could not produce its own likeness.¹² All univocal predications are, in the end, reduced to one first non-univocal analogical predication, which is being itself.¹³ That is the analogy of being: not a single flat sense of "is" spread across God and creatures, but an ordered community of reference, in which every creature's existence points back to the one in whom existence is not received but simply is.

Sources

if that were so, it follows that from creatures nothing could be known or demonstrated about God at all; for the reasoning would always be exposed to the fallacy of equivocation. Such a view is against the philosophers, who proved many things about God, and also against what the Apostle says: 'The invisible things of God are clearly seen being understood by the things that are made'
Summa Theologica Part I, Prima Pars
names are thus used in two ways: either according as many things are proportionate to one, thus for example 'healthy' predicated of medicine and urine in relation and in proportion to health of a body, of which the former is the sign and the latter the cause
Summa Theologica Part I, Prima Pars
This happens in two ways. First, according as many things have a relation to some one thing: thus in relation to the one health, an animal is said to be healthy as its subject, medicine as effective thereof, food as preserving it, and urine as its sign.
Summa Contra Gentiles Book I, God
Secondly, according as order or relation of two things may be observed, not to some other thing, but to one of them: thus being is said of substance and accident, in so far as accident bears a relation to substance, and not as though substance and accident were referred to a third thing.
Summa Contra Gentiles Book I, God
such names are not said of God and other things analogically in the first way, for it would be necessary to suppose something previous to God; but in the second way.
Summa Contra Gentiles Book I, God
Since an agreement according to proportion can happen in two ways, two kinds of community can be noted in analogy. There is a certain agreement between things having a proportion to each other from the fact that they have a determinate distance between each other or some other relation to each other... Again, the agreement is occasionally noted not between two things which have a proportion between them, but rather between two related proportions.
On Truth, Quaestiones Disputatae de Veritate, pp. 149–150
nothing can be predicated analogously of God and creature according to this type of analogy; for no creature has such a relation to God that it could determine the divine perfection. But in the other type of analogy, no definite relation is involved between the things which have something in common analogously, so there is no reason why some name cannot be predicated analogously of God and creature in this manner.
On Truth, Quaestiones Disputatae de Veritate, pp. 149–150
by the term 'wise' applied to man, we signify some perfection distinct from a man's essence, and distinct from his power and existence, and from all similar things
Summa Theologica Part I, Prima Pars
when we apply to it God, we do not mean to signify anything distinct from His essence, or power, or existence... this term 'wise' applied to man in some degree circumscribes and comprehends the thing signified; whereas this is not the case when it is applied to God; but it leaves the thing signified as incomprehended, and as exceeding the signification of the name.
Summa Theologica Part I, Prima Pars
whatever is said of God and creatures, is said according to the relation of a creature to God as its principle and cause, wherein all perfections of things pre-exist excellently.
Summa Theologica Part I, Prima Pars
The likeness of the creature to God is imperfect, for it does not represent one and the same generic thing.
Summa Theologica Part I, Prima Pars
the non-univocal agent is the universal cause of the whole species... whilst it is not univocal, nevertheless is not altogether equivocal, otherwise it could not produce its own likeness
Summa Theologica Part I, Prima Pars
all univocal predications are reduced to one first non-univocal analogical predication, which is being.
Summa Theologica Part I, Prima Pars