Tertullian is not saying that philosophy should be silent when it comes to things theological, or that philosophy and theology are about different subject areas, or that philosophy and theology somehow constitute incommensurate forms of discourse. He is saying that we should reject attempts to produce what he calls, "a mottled Christianity of Platonic, Stoic and dialectic composition."
In the following reflection I take Tertullian's intent to heart. I will not thereby produce a mottled Christianity. It does not follow, however, that not producing a mottled Christianity entails that philosophy has nothing to do with theology. In fact, philosophy has a great deal of relevance for theology, particularly as both disciplines were classically conceived and practiced. Since the time of Plato, western philosophy has been profoundly concerned with questions of semantics, with the meaning and truth of its expressions. Since the time of Aristotle, philosophy has been deeply concerned with logic, with entailments, compatibility and modality, that is, with what propositions follow from others, what propositions can be jointly true, and in what way these propositions are true. From both men philosophy learned about metaphysics; it learned to reflect upon being and to distinguish the different ways that something can be said to be. Clearly, talk of God presupposes positions in semantics, logic and metaphysics -- even if these views are not explicitly held or asserted.
Consider the following expressions comprising a primitive theological theory:
- God is incorporeal
- God is eternal
- God created the universe
- God has three persons
- God through Christ redeems fallen creation
The contextual theory of meaning, therefore, makes intelligible how students in a scientific discipline and scientists grasp the meaning, or sense, of scientific terms. On this account, understanding the meaning of a term is knowing how to determine its referent, or extension, at least in part. (See "Theoretical Terms in Science," The Stanford Encyclopedia of Philosophy (Summer 2013), Edward N. Zalta, (ed.) URL = <http://plato.stanford.edu/archives/sum2013/entries/theoretical-terms-science/>.When thinking of theology, it is clear that it too is a theory of a particular kind with some terms that are quite theoretical and some less so. For instance, the term 'human being' used in theology seems to make easy reference to the world, while the term 'creation' is more problematic. The first seemingly has a common reference in theology and sociology. The word 'creation', however, apparently refers to the universe as such within an overarching theological theory, but makes no reference at all within sociology -- unless it perhaps refers to the manuscript the sociologist is writing.
The term 'God' seems to have meaning within a particular theological theory. In (1) above, 'God' is predicated by 'incorporeal'. Is incorporeality "present in" God or "said of" God? If the former, then the being which is God has the property of not having a body in the actual world, but could have a body in another possible world. If the latter, then it is not possible that any being which is God could have a body.
From the standpoint of the philosophy of science, 'God' is a theoretical term naming a theoretical entity, a term that seemingly has incorporeality as part of its very meaning. Just as a bachelor is an unmarried male, so too is God incorporeal.
The same might be said about God's eternity. Perhaps it is essential for God to be eternal, that is, nothing that is God can fail to be eternal. If both eternity and incorporeality refer to God, then we might speak of a "conceptual tie or law": For any x, if x is God then x is eternal and incorporeal. But this is not a paradigmatic bridge law because it is not a biconditional; it does state in addition that for all x if x is eternal and incorporeal, then x is God. In addition, it does not "bridge" from observation events to the exemplification of a property by a theoretical entity.
If we do not, however, think of theological theory as having any bridge laws in the classic sense, but rather as constituted by a group of propositions having terms, many of which appear in a number of the propositions, we can speak of a term's meaning being a function of the way in which it appears in the other propositions in the theory. (What is predicated of the term and what the term is predicated of.) This implicit definition of the term then determines its extension.
Within our primitive theory, (1) and (2) presumably has a distribution of predication that differs from (3), for while predication of 'eternal' and 'incorporeal' in the theory does not allow for an x that is God to be predicated by 'not eternal' or 'corporeal', the x that is God can be predicated by 'creates the universe' or 'does not create the universe' because while one can have as a statement in the theory, 'did not create the universe at time t', one cannot have 'is not eternal at time t'. That the truth value of 'creates the universe' differs as a function of its temporal index, while the truth value 'is eternal' does not so differ, clearly shows that 'is eternal' means something quite different than 'creates the universe'.
Now consider the predicate in (4), 'has three persons'. To say that the x that is God has three persons is quite different than saying that the x that is a small company has three persons. Why? Because one rarely if ever would say that an x that is a causal agent -- like in (3) -- could ever have three persons. While a company could be said to be a group of people exhibiting certain relationships among them, God cannot be said to be a group in any sense, for the three persons having relationships among themselves is the simplicity of the one God.
Proposition (5) asserts that the x that is God causes it to be the case that the domain that God creates is now redeemed. This analysis of 'redeems the world' can be given a temporal characterization like 'creates the world', thus showing that these terms must have different meanings than terms like 'incorporeal' and 'eternal'. The phrase 'through Christ' adds further complication because it raises the question of whether 'God redeems' if and only if 'God through Christ redeems', and, if so, what does 'through Christ' add in meaning to 'God'. To show that 'through Christ' has a different meaning, one needs to show that 'God' and 'God through Christ' cannot be substituted with each other salve veritate throughout the entire theological theory.
What I am suggesting here is neither terribly original nor novel. I am merely suggesting that it might be instructive to look at theological theory with its theoretical entities in ways similar to how we might look at a physical theory having such entities. We might do this simply to get clear on the semantics of our theological language. What exactly is meant by a term appearing within a theological theory of a particular kind over and against a term appearing within a theory of another kind? Since we have fewer empirical moorings in theology than physics, it is useful perhaps to focus more deeply on what it is we might be meaning when employing language of the first kind.