Where does theology end and philosophy begin?
Answer by George Tsagdis
Aristotle gives three definitions of first philosophy or sophia (what would come to be known as metaphysics): i. the science of first causes (aitia) and principles (archai) of things, ii. the science of being qua being, iii. theology. A common problem of Aristotelian scholarship has been the harmonization of the three definitions. What does Aristotle mean when he defines the first philosophy as theology? What is this logos of God? First of all, what is God, if one can speak of God in accordance with the verb ‘to be’? In another famous definition Aristotle locates the essence of God in a thought that thinks itself (noeses noeseos). This thought is the first cause and the unmoved mover of the cosmos. Clearly then, if philosophy is the science, or knowledge, of the first causes it must think God: think the thought that thinks itself.
Aristotle is not alone in this tradition that recognises God as the very foundation of thought, a recognition strongly invested in the further Parmenidean premise that identifies thought and Being. In the history of philosophy God appears more often than not as principle and cause of both — and yet philosophy’s is a history of difference. It is interesting however to see that materialist philosophical thought has not always been severed from theology; the early example of Stoics, is telling in this regard.
All clearly hinges on the ways one attempts to think philosophy and theology. And yet, although God has died in so many ways and philosophy often wishes to think that it has detached itself from the discourse of this dead God, a discourse that constitutes its own history, this wish cannot be meaningful until a completely new thought is reinvented. It is important to trace what remains inextricable in the thought of philosophers who attempted most decisively to extricate themselves from theological themes, suppositions, tropes and so on (Wittgenstein, Deleuze, etc). First however, it is important to understand that the relation of philosophy and theology is not akin to that of any two disciplines, defined principally by their scope and methodology. If the first task of thought is to think itself, philosophy will, in the Aristotelian sense, forever remain divine.
Answer by Massimo Piglilucci
Distinguishing theology from philosophy is a tricky business. Broadly speaking, it is an exercise in conceptual demarcation, similar to the attempts to separate, say, science from pseudoscience , or philosophy itself from science. On the one hand, it is bound to fail if we understand such demarcation to be characterized by sharp, clear-cut boundaries. On the other hand, it seems obvious that there are differences between theology and philosophy (or science and pseudoscience, or science and philosophy), so that it makes sense to ask the question.
To begin with, then, it may be helpful to see that whatever criteria may turn out to be useful in such efforts do not form a set of necessary and jointly sufficient conditions. Take, for instance, one possible definition of a triangle: a polygon with three edges and three vertices. Having those characteristics is both necessary (without them, a geometric figure is not a triangle) and sufficient (they are enough to separate triangles from every other geometric figure). Philosophers have long agreed that complex concepts such as theology and philosophy (or science and pseudoscience) are simply not amenable to this kind of definition.
What then? We could adopt what is called a ‘family resemblance’ approach, famously advocated by Wittgenstein in a similar context (in his example, the definition of a game). Certain concepts (games, theology, philosophy) are loosely defined by a series of ‘threads’ that may or may not be instantiated in every single application of the concept. For instance, while games often have rules, they are set up as competitions, they are engaged in for fun, and so on, there are some games that do not have all those characteristics (e.g., in solitaire one doesn’t play to ‘win’), as well as other activities that may displayed them, and yet are not games (e.g., one can go hiking for fun, but hiking isn’t a game). Wittgenstein then suggested that the way we know what a game is hinges on the fact that we are able to point to certain activities and say ‘that’s a game, that’s not a game,’ which sometimes means that there will be situations were we are genuinely uncertain, not because we are ignorant of something, but because the activity in question truly has some, but arguably not enough, of the characteristics of a game.
How do we apply this approach to the question of the relationship between theology and philosophy? Well, both disciplines share a number of characteristics in common, including the fact that they are not directly concerned with empirical evidence (i.e., they are not sciences), they do not usually use symbolic reasoning of the type associated with math (though they may express some of their propositions in logical symbolism), and they both are best done by presenting formal or informal arguments in favor of certain conclusions, arguments that are in turn based on certain assumptions about whatever the subject matter at hand happens to be.
The main difference between theology and philosophy, then, seems to be that theology begins with a set of assumptions that philosophy does not have to, and normally does in fact not, accept: that there is a supernatural realm, featuring one (or more) entities called gods, who have a certain role in human affairs (and played a crucial one in the beginning of the cosmos), and who have a number of characteristics (e.g., they may be benevolent, all powerful, and all knowing, for instance). By contrast, much modern philosophy is carried out from a naturalistic perspective, i.e., without regard to (or even while downright denying) the existence of transcendental realms of the type that theology takes for granted. (That said, some philosophers do accept other types of transcendental realms, for example those that subscribe to mathematical Platonism  or modal realism .)
What further complicates the issue of separating theology from philosophy is that historically there was no such distinction, at the least during most of the Middle Ages in Europe. Certain important figures of the history of Western philosophy, from Augustine to Thomas Aquinas, were theologians. (Just like, say, important figures in philosophy were also scientists: Descartes, for instance.)
However, nowadays philosophy and theology university departments tend to be separate (and even when they are part of a single academic unit, often function effectively as separate), and theological and philosophical professional conferences and publications are also distinct. This seems to suggest that – while there are still areas of overlap (most prominently, in the field of the philosophy of religion), the relevant academic communities themselves seem to increasingly endorse the idea that theology and philosophy are different fields of inquiry. Of course, a more radical possibility is for a naturalistic philosopher to argue that – because theology is based on false assumptions (about the existence of the supernatural) – it is really an example of pseudo-philosophy, just like, say, astrology is an example of pseudo-science (because based on the false assumption that distant celestial bodies have a direct effect on human affairs).
 See, for instance: Philosophy of Pseudoscience: Reconsidering the Demarcation Problem, edited by M. Pigliucci and M. Boudry, University of Chicago Press, 2013.
 See: Mathematical Platonism, by M. Pigliucci, Philosophy Now, 2011.
Answer by Tony Boese
To answer this question, I think it would be best to start by looking at the words themselves, and their respective etymologies. In particular, consider the first part of each conjunct. For Theology this is theoi which centers on that which pertains to the gods. In full, Theology would be, at least roughly, the study of the gods and their accoutrements and hangers on (demi-gods, angels, mythical creatures, etc.). In contrast, Philosophy begins with philos, which centers on wisdom. In full, Philosophy is the love of wisdom and all that we can get from and with it. Granted, wisdom is a bit of a term-of-art for we Philosofolk; however, this Wisdom/ God(s) divide should be salient nonetheless.
Of course, the natural next question is whether or not what it says on the tin is of any use. I think it is, and I think I have a sense of why many might think it is not. In short: Philosophy and Theology cover a lot of overlapping materials; however, what is less seen is that we do this in different ways and often for different reasons. For Theology the justification has its bedrock in what (the) G/g o/- d(s) (to cover as many bases as I can!) think and want. Even when the subject at hand is the unilluminated writings of other people, as opposed to scripture for example, it is likely that their subject is what said divine person(s) wants, or thinks. In contrast, the justification in Philosophy is supposed to be reason and logic. The argument must find its way back to a truth. It is best if it is a non-contentious claim, but any suitably stable and defensible claim will do. Up to a point in history, the (e.g.) Will of God was accepted among these grounding truths, and was a well touted one at that. In this period, which is one to which most people are exposed when taught philosophy (big name, historic texts, up to the enlightenment, as opposed to more contemporary pieces), is likely the locus of the equivocation. That said, if one tried to break philosophical ground on the back of scripture and divine will alone today, it would most likely not be well taken by the academy,
On a less rigorous note, the role of experience might be an important consideration. This is something mostly beyond my wheelhouse, both academically and experientially; however, I have heard it said and find it interesting if not also compelling, that Theology has a key experiential component. Theology is done based on experiences and reflections, both divine and mundane, both our own and others. Philosophy, in contrast, though often having an experiential element especially when resting on intuitions, can and some say should be done completely devoid of this. One can do philosophy entirely in the abstract and hypothetical, even reaching practicable conclusions via this method.
Finally, for sake of being through, I feel it important to note that there are possible exceptions wherein Philosophy and Theology are virtually exchangeable, or at least are directly in dialogue. A big one that comes to mind is Just War.