Thomas Aquinas summed up a long tradition when he said that philosophy is theology's ancilla, its maidservant. That's an apt description, and applies as well to natural science, social science, poetry, literary criticism, history, etc. etc. Philosophy has a special role only because her work often resembles theology's, and because she so regularly tries to take over as mistress of the house. Theologians have to learn her tricks so that they can keep her in her proper place.
I offer a few examples, provoked by my reading of Steven Duby's Divine Simplicity. Duby isn't a bad example of the theological use of philosophy; on the contrary, he uses philosophy to tease out dogmatic ramifications form his detailed and rich biblical expositions. (This makes his book far more satisfying than James Dolezal's God Without Parts, which includes virtually no discussion of Scripture.) Still, Duby does sometimes slip into philosophy's traps.
1) Philosophies differ. Everyone knows that, and Duby explicitly chooses to expound simplicity in Thomist/Aristotelian categories. But it seems that he sometimes forgets the variety of metaphysical systems.
2) Duby criticizes recent writers who claim that God has accidents partly on the grounds that the characterizations they call "accidents" aren't accidents in a strict, Aristotelian sense. Accidents aren't merely qualities or properties somehow added to a substance, but perfecting additions. Since God is always already perfect, He can have no accidents. The recent writers that Duby criticizes define an accident as any property or characterization that's contingent; thus, they argue, "Creator" names an "accidental property," since God wasn't Creator before He created.
But who's to say which definition of accident is "right"? So long as someone stipulates a definition and uses the term with some consistency, why would it matter if the definition differs from Aristotle's? This can quickly become a fruitless argument over terminology.
3) Philosophy bewitches by her rhetoric. She makes us think that speaking in her dialect is more precise or profound than speaking in the poetic dialect of Scripture. I contend, on the contrary, that the Scriptural talk of God is the most precise and adequate language we can have. It's God's own talk about Himself.
4) Philosophy bewitches by her rhetoric in another sense. She bewitches us into depersonalizing God - rhetorically, if not materially. She fools us into talking, as Duby does, about things like "the impinging of the divine essence in God's historical action on different objects with different effects" (185) rather than, say, about Yahweh God of Israel visiting His people. I suspect that Duby means to say that; but beware the rhetorical bewitchment.
5) Philosophy makes us assume things are established that aren't established. Duby regularly cites theologians and philosophers (e.g., Thomas himself) who say that unity is superior to diversity. Thomas: All created perfections pre-exist in God "but he has these in a mode more excellent to all things, because in him they are one, but in others they have diversity" (184). On what grounds do we assume that having things "in one" more excellent than having them multiply? Philosophy wants us to take this as a given; but it needs to be argued for.
Another example: Arguments in favor of simplicity often appeal to the relation of parts and whole. It's assumed that parts must be lesser than the whole. That's obvious within certain systems, not at all obvious within others.
Mathematicians have argued, for instance, that there are multiple infinities and they come in different sizes. Some infinities are part of other infinities, while still being equal in size to the "whole" of which they are part. The set of natural (positive) numbers is a countable infinity, as is the set of integers (positive and negative numbers, plus zero). They are the same size, even though the set of natural numbers is a subset or part of the set of integers.
With this in mind, arguments like "God cannot be made of parts because parts are less than a whole" lose their force.
6) Duby acknowledges that some of the metaphysical conclusions he draws from the Bible are implicit. The danger is that the implied metaphysics might become the controlling paradigm, determining the explicit statements of Scripture. If anything, it would seem that priority should be given to the latter.
7) The transition from biblical exposition to metaphysical elaboration can be bumpy. Duby argues in this fashion: Scripture emphasizes God's aseity and independence; and this implies simplicity. But this involves a process of translation from biblese into the categories of metaphysics. That's where the bump occurs, because the arguments end up being in this form: "Scripture teaches X; if we translate X into the Thomist/Aristotelian framework, X implies simplicity."
But that form of argument doesn't prove anything about what the Bible actually teaches. It only says that if we translate biblical claims into the Thomist framework, we get simplicity. But we already knew that. What we want to know if the biblical material might in some way challenge the Thomist framework.
8) Philosophy seduces us into distinction-mongering. Metaphysics leads us to conclude X; the Bible introduces some data that disrupts X; instead of reconsidering X, we introduce system-saving distinctions. System-protective distinctions are certainly useful; perhaps they're inescapable. But we should be wary. In the main we should keep to distinctions that force themselves on us by the realities of God, creation, and the Bible.
If we find ourselves multiplying distinctions, we should reconsider the premises that drove us toward these complications. We should suspect that the maidservant might be trying to take over again.