Here’s a narrative you may have come across if you have received a history of philosophy from a historical-theological focus:
From a theological perspective, the most pertinent philosophy began with Augustine and Boethius, kickstarting much of the philosophical discussion during the medieval period that would interact with Aristotle, Plato, and the Stoics. During this period, much of the philosophical discussion overlapped with theological issues, where logic, ontology, epistemology, and other sub-disciplines were developed in concert with developments in theology proper, anthropology, etc. This became especially true after the rediscovery of Aristotle’s works, where many Islamic philosophers were on the cutting edge of this rediscovery and incorporated Aristotle’s philosophy into their theology, and this attracted thinkers in the Jewish and Christian traditions to follow their lead. The tension between Aristotle and theological orthodoxy continued for a few centuries until the Enlightenment bomb dropped. Descartes’s skepticism and epistemological focus started a gradual but accelerated separation between philosophy and theology. That separation would accelerate even more with Hume and Kant, and would reach its climax in the 20th century with the logical positivist claim that metaphysical and religious questions are literally nonsense. As more and more philosophers in Europe were wrestling with a post-Kantian world, and truth itself gave way to subjective perspective, postmodernism emerged and gained a foothold, allowing Derrida, Foucault, and others to gain influence in the philosophical world and eventually into the public mind. And that is where we find ourselves today — reeling from postmodernism, post-truth, and a philosophical climate that is overwhelmingly atheistic.
The problem with this kind of narrative is not that it’s a sweeping summary; summaries are needed at times, and they will inevitably leave out details and nuance. But this summary leaves out one of the most fruitful philosophical streams from the past 150 years: the analytic tradition.
I was recently talking about the history of philosophy with a philosopher who has been teaching for a few decades, and he said something that has stayed with me: many of the more popular philosophical luminaries like Kant, Heidegger, Wittgenstein, and Derrida are included in summaries like the one above because their (translated) work is largely non-technical and therefore relatively accessible. Because much of the analytic tradition uses technical language and tools related to logic, few historians (understandably) outside that tradition can access the work and achievements within that stream. That means historical summaries at a popular level and historical sweeps from within other fields (like theology) will inevitably be incomplete and uninformed.
This is important because of all the concepts and ideas that have been developed within that ignored analytic stream; concepts and ideas central to theology. I have mentioned before that the idea of ontological relations underwent a focus and development in the late 19th century. Similarly, no one can talk about the infinite in the same way after the work of the German mathematician (and Lutheran) Georg Cantor, who developed set theory and demonstrated that there are different kinds of infinity. (If anyone can make infinity interesting, it’s David Foster Wallace in his 2003 book on the topic.) Understanding the nuances of infinity helps us avoid defining infinity in simplistic terms like “limitless” or “neverending,” and it helps us fill out theologically loaded ideas like an infinite series of events. (I will ignore the complexities of the metaphysical status of things like events.) You would think a seismic shift in how infinity is understood would put Cantor perennially alongside Kant, Hegel, and other renowned fellow Germans, but the technical nature of his work limits its accessibility, so its significance has become muted from popular histories.
In the same way, Cantor’s contemporary and fellow German Gottlob Frege helped create a new, self-conscious discipline of philosophy of language as he also worked in mathematics. The advances and explosions happening in (mathematical) logic and philosophy of language during the late 19th century continued into the 20th century, marking that century as one largely focused on those two disciplines within the analytic stream. Frege’s work helped distinguish elements within language like sense, reference, and meaning, developing these ideas formally through logic, and connecting it to the precision of mathematics. He was making great strides until a young Bertrand Russell, who was a fan of his work, wrote him what is now an infamous letter pointing out a contradiction in his system, effectively ending Frege’s career and prestige. But that’s a story for another time.
And I could mention the Polish logician Alfred Tarski, whose early 20th century work on formalizing the concept of truth has now become standard within classical logic. Or Kurt Gödel, whose theorems you would need to be familiar with when discussing consistency and provability. Later on, the developments within modal logic and possible world semantics would generate immense discussion that involved ideas like necessity and essence — concepts crucial to several theological ideas like God’s existence and nature, the Trinity, and counterfactuals (think about what makes hypothetical universalism hypothetical).
So if a theological historian seeks to understand the history of these ideas — infinity, truth, essence, necessity, etc. — from within both theology and philosophy, leaving out analytic developments will make for a warped, uninformed overview. Outside philosophical circles, quoting Aristotle or Kant can be mistakenly viewed as an intellectual achievement itself; inside philosophical circles the story is quite different. If asking the systematic question of how we are to understand a concept like possibility, quoting Aristotle or a 17th c. theologian on the topic won’t cut it systematically or historically.