In his epic work Summa Theologiae (1a.13.1-6, 12), Thomas Aquinas first begins his discussion on religious language by asking a number of questions as to whether or not we have “words for God”:
Can we use words for God?
Do any of the words we use for God expresses what he essentially is?
Do some of the words we use for God apply to him literally, or are they metaphorical?
Are these words used for God synonymous?
Are words used of God and creatures univocally or equivocally?
If we say they are used analogically, do they apply primarily to God or to creatures?…
Can we make affirmative statements about God? 
He thus begins to engage these questions with the following objection: “It seems we have no words for God.” Aquinas then outlines the strongest three arguments for that objection:
- (1) For  pseudo-Dionysus says: of him there is neither name nor opinion. And Proverbs 30 asks: What is his name or his son’s name? Do you know?
- (2) Moreover,  nouns are either abstract or concrete. Neither are appropriate to God: concrete nouns because he is simple, abstract nouns because they don’t express complete subsistent things. So no nouns apply to God.
- (3) Moreover,  nouns express sorts of things, verbs and participles are tensed, pronouns are either demonstrative or relative. None of this is appropriate to God, who is without qualities or incidental properties, exists out of time, can’t be ostensively demonstrated to our senses, nor referred to by any pronoun referring back to a noun or participle or demonstrative pronoun. So no sort of word can apply to him.
It is here that we see the beauty of the scholastic method of disputation at work. As Timothy McDermott explains, “the structure he adopts is that of sets of disputed questions, though each article in a set is very much simplified in its microstructure. The simplification he adopts generally [ … ] limits the objections to three and the arguments in favor to one, and he keeps the summing-up [ … ] to a modest length by multiplying articles rather than by dealing with too many points within each one” .
Aquinas’ Reply to the Objections
Thus, Aquinas limits himself by allowing only one reply to the three objections. In this reply Aquinas quotes Aristotle where he writes that “words express thoughts and thoughts represent things” . Hence, words correspond immediately to things by way of our own mental conceptions. (i.e., “we talk about things in the way we know them.”) It should be noted here first that intellectual cognition according to Aquinas is dependent on sense experience. (e.g., “It is natural to human beings to attain to the intelligible though sensible things.”) Jan Aertsen (1997) comments on this subject saying that
[s]ystematic knowledge extends only as far as sensory cognition. Of course, the senses are not the total cause of all our knowledge, but they do provide the indispensable material from which the intellect abstracts the intelligible content. From this it follows that human beings cannot know the essence of a substance that is not perceptible by the senses. .
It is thus Aquinas’ position that “in this life we cannot see God’s substance but know him only from creatures: as their non-creaturely and transcendent” . This gives us gateway to Aquinas’ solution to the problem of religious language:
So this is where our words for God come from: from creatures. Such words, however, will not express the substance of God as he is in himself, in the way words like human being express the substance of what human beings are in themselves, expressing what defines human beings and declaring what makes them human beings; for the meaning of a word is the definition of some thing. .
Hence, in response to the three objections:
- to (1): “God is said to have no name or be beyond naming because his substance lies outside what we understand of him or can express in words.”
- to (2): “Because our knowledge and our words for God come from creatures, the words we use for him express him in ways more appropriate to the kind of creatures we know naturally, and these, as we have said, are material creatures. In such creatures subsistent wholes are composed [of formed material], the form not being a subsistent whole itself but determining what subsists. So all our words for expressing subsistent wholes are concrete terms, appropriate to composite things; whereas to express the non-composite forms we use words that don’t express them as subsistent but as determining what subsists: as whiteness, for example, names what makes things white.” 
In reply to objection (2), Aquinas’ statement here becomes important:
Now God is both non-composite and subsistent, so we use abstract terms to express his lack of composition and concrete terms to express his subsistence and wholeness. But neither way of talking full measures up to his way of existing, for in this life we do not know him as he is in himself.
Since Aquinas likewise argues that when we see an effect, we have a natural desire to inquire into its cause. This natural desire however will not come to rest until we reach the First Cause, “namely the divine essence itself” . We are therefore inadequate in our forms of language to meet these attributes of non-composition and subsistence in respect to God. However, our best shot at achieving a functional form of religious language can be found in the following options:
- (1) Analogical Language
- (2) Univocal Language
- (3) Equivocal Language
Explanations of the Three Forms of Religious Language
In respect to (1), it was Aquinas’ proposal through the principle of analogy that the fact that God created the world points to a fundamental “analogy of being” (analogia entis) between God and the world. Alister McGrath (2001) writes:
There is a continuity between God and the world on account of the expression of the being of God in the being of the world. For this reason, it is legitimate to use entities within the created order as analogies for God. In doing this, theology does not reduce God to the level of a created object or being; it merely affirms that there is a likeness or correspondence between God and that being, which allows the latter to act as a signpost to God. A created entity can be like God, without being identical to God. 
Where Aquinas believed that “words correspond immediately to things by way of our own mental conceptions” is where his point of divine self-revelation is made clear: namely that this kind of revelation makes good use of images and ideas that tie in with our world of everyday existence, “yet which do not reduce God to that everyday world” .
(2) Univocal language however can be understood as language that means the same thing in all situations (e.g., “black cat,” “black hat,” black mat,” “black rat,” etc). Aquinas draws this objection in Article 5, Question III where he discusses Aristotle’s comment “that a measure must be generically one with what it measures” . Thus, Aquinas seems to follow the objection to say that “God is the first measure of everything, and therefore generically one with creatures; so something can be said univocally of God and creatures” . This would seem to imply that if we say “that lesson was good” then good means something different from saying “God is good,” since God is perfect and infinite. Thus, Aquinas rejects univocal language by a further statement saying that
[n]othing can be said univocally of God and creatures. For effects that don’t measure up to the power of their cause resemble it inadequately, not reproducing its nature, so that what exists in simple unity in the cause exists in the many various forms in the effects: the uniform energy of the sun, for example, produces manifold and varied forms of effect on earth. And in the same way, as we have said, all the many and various perfections existing in creatures pre-exist in God in simple unity. 
(3) Equivocal language as defined by Aquinas means “[w]hen the same word is used but with different meanings” . This form of language becomes problematic as well, since, taking for example, if we were say that “God is good” meant something completely different from any other good then God would be unintelligible (i.e., we couldn’t understand him). Thus, Aquinas also rejects equivocal language.
-  from Aquinas: Selected Philosophical Writings (Oxford University Press: 1993) p. 214
-  McDermott, Aquinas: Selected Philosophical Writings (Oxford: 1993) xx.
-  Int. 1. [1.16a3].
-  Jan Aertsen, Aquinas’s Philosophy in its Historical Setting in The Cambridge Companion to Aquinas (Cambridge University Press: 1997) p. 32
-  From Aquinas 1993, p. 215
-  Ibid.
-  Ibid., pp. 215-216
-  J. Aertsen, 33
-  Alister McGrath, Christian Theology: An Introduction (Blackwell: 2001) p. 253
-  Ibid.
-  Aquinas 1993, p. 223
-  Ibid.
-  Ibid., p. 224
-  Ibid., p. 223