There are three things to note about knowledge by analogy in general before discussing knowledge of God by analogy to creatures. First, an analogy is a means to real knowledge of a thing. In every analogy something is known by comparison to something else to which it has a similarity. Since they have a real similarity, what is being said about them is not a pure equivocation. Unlike “bark of a tree” and “bark of a dog,” which are merely the same sounds used to signify different ideas, terms used analogously can be reduced to one principle. For example, we say “healthy” of a fit man, a nourishing steak, and a robust complexion. This is not simply the use of the same sound to signify completely different ideas - there is one reason for using “healthy” in all cases, that it signifies some relation to well-being. Therefore, calling a piece of dead meat healthy is actually informative in light of the already known healthiness of a man.

Second, an analogy is not identity. However real the similarity may be between significations, they still are not the same significations. The “healthy” said of man is not the same as the one said of steak or of color. Although there is one principle of all uses of the word, the relation to well-being, each case employs a different relation. The man is healthy, because he has health formally in him; the steak is healthy because it has the power to be a material and agent cause of well-being in something else; complexion is healthy because it is an effect of well-being. Thus, the analogous uses of a word are neither purely equivocal nor purely univocal.

Third, there may be an order among analogous senses of a word. Since formal well-being is the final cause toward which healthy agents and matter are ordered, and since a healthy complexion is an accidental consequence of a healthy man, “healthy” is primarily applied to a man. Nevertheless, a derivative use may be more known to us than a more primary use. For example, we use a healthy complexion as a sign of a healthy man because it is more obvious to us. This order of intelligibility, according to nature or according to us, is especially clear in those cases in which we can know fully one use of a word but not another. For example, we know prime matter by an analogy with the matter of an artifact:

The underlying nature, however, is understandable according to analogy. For as bronze is to statue or as timber is to bed or as matter and the formless before it takes on form is to whatever else has form, so is this underlying nature to substance and “this something” and a being.¹

We know that matter which underlies substantial change exists because we know matter which similarly underlies accidental change. Still, we can have no direct experience of prime matter, since in itself it is entirely without form and lacks intelligibility. Therefore, when we use “matter” to signify prime matter, we do not have comprehension of what that signification means. We only know that prime matter has to substantial form, which is known, a similar relationship as that of secondary matter to accidental form, which are also known. Therefore, it is manifest that the use of “matter” to signify prime matter is less known to us than other uses. It is also true in this case that prime matter is less knowable by nature, because it lacks act, which is what gives things intelligibility.

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1. Physics, 191a 10-12 (Bk. 1, Part 7)