Philosophers have gotten something of a bad reputation for widespread—and perhaps closed-minded—atheism. The reality, however, is quite otherwise. We will address the reputation of closed-mindedness towards the end of this chapter. But first, we’ll address the historical point. For most of their history, philosophy and religion have almost always been intertwined in one way or another, and the vast majority of philosophers have had some kind of religious beliefs, oftentimes central to their philosophy, whether or not they have made the links explicit. And this is not without good reason. Though their methods (sometimes) differ, philosophy and religion have always shared a number of similar goals in terms of seeking answers to life’s “Big Questions,” questions about the ultimate nature of reality, our purpose or place in the world, the meaning of life and how we should live it. In Plato’s Republic, Socrates famously says, “It is no small matter we are discussing but the very question of how we are to live our lives” (Book I, 352d). Many religious believers would say the same thing when discussing their religious beliefs.

Indeed, outside of Western culture, where a sharp division has developed between philosophy and religion as a result of the Enlightenment, it is sometimes hard to tell the difference between the two. Scholars agonize over whether Confucianism is “really” a religion or “only” a philosophy—or maybe neither one (Taylor 1990; Adler 2006; Sun 2015). Likewise, whether Buddhism fits neatly into either category or maybe into both at the same time (Prebish et al. 2019). But even in the Western tradition, the division between philosophy and religion was not always so sharp prior to the Enlightenment, as we will see.

If you are new to philosophy, many of the philosophers discussed below may be unfamiliar to you. That’s OK! The point here is not to memorize names and dates, but to get a feel for how a representative sample of many of the “heavyweights” in the history of philosophy have interacted with religion and how the two have, historically, not always been at odds with one another but have rather been intertwined, mutually influencing one another.

Ancient Greek Philosophers

Ancient Platonists, if asked to summarize the essence of the philosophy of Plato (c. 429-347 BCE), would answer that it was a way of life directed towards homoiosis theou—becoming like God (Annas 1999, 52 ff.). At various points in Plato’s dialogues, his descriptions of philosophy and of wisdom sound much more like descriptions of out-of-body experiences than like today’s notion of “thinking deeply about important questions.” For example, in Phaedo, Socrates says, “I am afraid that other people do not realize that the one aim of those who practice philosophy in the proper manner is to practice for dying and death…” and then defines death as “the separation of the soul from the body” (Phaedo 64a). He goes on to discuss how the true philosopher is not concerned with things connected to the body (including sense perception), but with the soul and trying to get the soul to be “by itself, taking leave of the body and as far as possible having no contact or association with it [the body] in its search for reality… the soul of the philosopher most disdains the body, flees from it and seeks to be by itself.” Later Socrates continues, “if we are ever to have pure knowledge, we must escape from the body and observe things in themselves with the soul by itself” (Phaedo 66d-e). While there are other ways to interpret such passages, there is a long tradition of reading Plato as talking about something like an out-of-body experience that opens up some sort of mystical knowledge about reality and even God. Certainly, something along those lines is how he was read by the so-called neoplatonists like Plotinus and Porphyry.

What we today call the “metaphysics” of Aristotle (382-322 BCE), he himself famously called “theology” (Metaphysics XI.7, 1064b1). Prior to Plato and Aristotle, the writings of the pre-Socratics (Greek philosophers prior to roughly 400 BCE) were filled with speculations about the nature of God, or the gods. For example, Thales (624-546 BCE) claimed that “all things are full of gods” (Kirk et al. 1983, 95). We know very little about Pythagoras (570-490 BCE); it’s doubtful he actually discovered the theorem named after him. But one thing we do know about him is that he taught his followers to believe in reincarnation and engage in various mystical practices (Kirk et al. 1983, 214 ff.). And Parmenides (515-450 BCE) presented his philosophy in the form of a long poem about a spiritual vision he had, in which secret truths were revealed to him by divine beings (Kirk et al. 1983, 239 ff.).

The Stoics believed the universe was guided by divine Logos. While “Logos” in Greek Philosophy often just means human reason or an argument, the word is also the Greek equivalent of the Hebrew “Davar” or Aramaic “Memra,” (the divine “Word” of God) which, in the latter parts of the Hebrew Bible and in the Targums (Aramaic translations or paraphrases of books of the Hebrew Bible), began taking on many of the characteristics associated with God. (For example, in the Targums, it is the Memra who delivers the Israelites from Egypt  and makes a covenant with them, and so forth.) And although the Stoics are considered a school of Greek Philosophy, the first Stoics happened to be Semitic immigrants from the East (Lightfoot 1894, 273, 299), so their view that the world is governed by a divine “Word” is especially noteworthy for its connection to Jewish thought.

This term “Logos” later shows up in the Jewish philosopher Philo of Alexandria (c. 20 BCE-50 CE), who describes the Logos as a kind of “second god,” the “first-born Son of God,” and the “eldest angel” (archangel) (Philo 1993, 834; 247). Philo’s thoughts about the Logos show deep familiarity with both Plato and the Stoics. Traces of this “Logos Theology” are to be found in Jewish Midrash as well (American-Israeli Cooperative Enterprise, n.d.). It’s perhaps unsurprising that Philo shows familiarity with the philosophy of his day, being from Alexandria, Egypt, one of the greatest centers of philosophical learning in the ancient world. The Gospel of Matthew claims that Jesus also spent time in Egypt as a boy (Matthew 2:13-21), which, if true, would almost certainly have been in Alexandria, where the vast majority of Jews living in Egypt at that time resided. This would place Jesus in the same city as Philo at just the time Philo’s career there was flourishing. We also see Philo of Alexandria’s term “Logos” playing an explicit, central role in a number of New Testament works, the most famous being the prologue to the Gospel of John (1:1): “In the beginning was the Logos, and the Logos was with God, and the Logos was God.” The term “Logos” has been described as a kind of bridge between Jewish and Hellenistic thinking (Boyarin 2011, 546-549).

Numerous individual passages in the New Testament, as well as the entire epistle to the Hebrews, also show influence on a number of points either directly from Philo or else some common source from which Philo and the New Testament authors must both have been drawing (Siegert 2009, 175-209 passim; Runia 1993, 83, passim). For example, the author of Hebrews famously downplays the importance of the earthly temple in Jerusalem in favor of a heavenly temple, of which the earthly temple is merely a “copy and shadow”:

[They] serve the copy and shadow of the heavenly things, as Moses was divinely instructed when he was about to make the tabernacle. For He said, “See that you make all things according to the pattern shown you on the mountain.” (Hebrews 8:5)

The talk about “copy and shadow” recalls Plato’s famous Analogy of the Cave in Book VII of the Republic, where prisoners are chained up, facing a wall, unable to see anything except “the shadows of copies of things,” which they mistake for the truth (514a-c ff.). The talk about making all things “according to the pattern” recalls Plato’s discussion of the “craftsman” or “demiurge” (creator of the universe) in Timaeus (28a6). Likewise, Hebrews 11:10 describes Abraham as searching for “the city having the foundations, whose artificer and constructor [is] God,” where “constructor” is Plato’s term “demiurge” used for the creator in the Timaeus.

Plato also famously divides all of “being” into two realms: (1) the “visible” (particular, concrete things like people, trees, animals, etc.), which is temporary and perishable, and (2) the “invisible” (the abstract ideas or “Forms” or essences of things), which is eternal and unchanging (e.g., Phaedo 79a-b). St. Paul seems to explicitly make use of this framework in 2 Cor. 4:18: “For the things which are visible are temporal, but the things which are invisible are eternal.” Again in Timaeus, Plato describes his highest principle, the “Form of the Good” as “the Creator and Father of all” and thus, in a sense, even higher than both of these visible and invisible realms (Timaeus 28c). Again, St. Paul also speaks of God creating “all things, visible and invisible” (Col. 1:16) in Christ. And famously, along with St. Paul and other New Testament authors, even Jesus himself is recorded as referring to God as “Father,” a title very rarely used for God in the Hebrew Bible or the Jewish tradition more generally, but appearing in Plato and repeated constantly in the New Testament. Another Platonic theme found in the New Testament relates to Plato’s saying that to “find” God is difficult, and “to declare him to everyone is impossible” (Timaeus 28c). Elsewhere he repeats that the highest principle is too difficult to grasp, so we must reason instead about His / Its “Offspring” instead (e.g., Republic 506e-507 and 508b-509). We then find in multiple New Testament authors this familiar Platonic idea that we cannot have direct knowledge of God (“the Father”) but must have recourse to His “Offspring” or “Son” for any knowledge we would have of Him, the Son being an “image” of the Father. (John 1:18; John 14:9; Col. 1:15; 1 Timothy 6:16; Hebrews 1:3; 1 John 4:12).

Does all this mean Plato was the source of these ideas in the New Testament? As we’ve seen, it would be difficult to deny that several New Testament authors make use (apparently intentionally) both of Plato’s thoughts and his vocabulary. As to whether Plato was the source of any of the New Testament authors’ thoughts, however, it’s hard to say, and scholarly debate continues. Of course, there are also deep differences that must be acknowledged as well. But while questions about sources and directions of influence may be debated, one thing is for certain: there was no separation into two distinct compartments of “philosophy” versus “religion” at this point in history. Thinkers at this time did not see two categories here, but one.

Modern Philosophy

After the armies of the Fourth Crusade sacked the Eastern Christian city of New Rome/Constantinople in the 1200s and brought back precious ancient manuscripts, Western Europe saw the Renaissance blossom in the following century (1300s). After the eventual fall of Constantinople in 1453 (which led many Greek scholars to flee west and bring more knowledge and manuscripts with them), the arrival of Europeans in the Americas in 1492, the rise of Protestantism beginning in 1517, and the Scientific Revolution (perhaps datable to Copernicus’ publication of On the Revolutions of the Heavenly Spheres in 1543), we come to the Modern Period. The rapid pace of discovery of new knowledge and the overturning or questioning of previously-held beliefs from the mid-1400s to mid-1500s led to a period in which Classical learning began to be questioned, doubted, and interrogated to a growing degree. Not surprisingly, and despite being in many ways revolutionary compared to Ancient and Medieval thought, Early Modern Philosophy was still deeply concerned with religious questions.

The philosophies of the great Rationalists—René Descartes (1596-1650), Baruch Spinoza (1632-1677), and Gottfried Wilhelm Leibniz (1646-1716)—were all bound up in many ways with their respective Catholic, Jewish, and Protestant theologies. Descartes’ famous Meditations are largely concerned with proving the existence of God and the distinction of the body and soul. Spinoza’s Ethics argues for his version of pantheism. Leibniz wrote versions of both the Cosmological and Ontological arguments

Turning from the Rationalists to the British Empiricists, John Locke (1632-1704) was a deeply religious man and authored arguments for God’s existence. Even his political philosophy begins from the premise that we are all God’s property (which he seems to have meant quite seriously), for example, in the Second Treatise on Government 2.6 (Locke [1689] 1980, 9). George Berkeley (1685-1753) was actually a bishop in the Church of England, and a key aspect of his philosophy of “idealism” was the idea that, since matter doesn’t really exist, only minds and ideas do, there has to be one very powerful mind (God) that constantly perceives all things and holds them in existence. Last  among the three great British Empiricists, only David Hume (1711-1776) could reasonably be called an atheist though this label was more of an accusation by his opponents. His views on religion have been more accurately described as “attenuated deism.” In other words, he seems to have held something like the belief that there is some kind of Creator, who may possibly be something like a Great Mind, but who is not likely to be directly concerned about anything that happens in the world, at least as far as anyone would have any way of knowing (Gaskin 1987, 223 ff.).

Immanuel Kant (1724-1804), whose “critical” philosophy was largely a response to Hume’s skepticism, described his project in The Critique of Pure Reason (B xxxi) as a way to “deny knowledge, in order to make room for faith” (Kant [1781] 1998, 117). While the philosophy of Hegel (1770-1831) is today often summarized in the triadic phrase, “thesis-antithesis-synthesis,” Hegel’s own conceptualization of his philosophy had much more to do with the Christian doctrine of the Trinity (as he interpreted it), which he explicitly stated he was trying to revive, since the theologians of his day had, in his view, abandoned it (Schlitt 2012; Schlitt 2016).

Finally, although there had been atheist philosophers before, it is only really in the 1800s, with Karl Marx (1818-1883) and Friedrich Nietzsche (1844-1900), that atheistic philosophies begin to gain what will turn out to be a more solid and lasting foothold in the intellectual history of the West. But of course, it would be completely wrong to say that Marx or Nietzsche were not concerned with religious questions. Rather, they were both deeply concerned with questions about religion—they simply came down on the negative side of those questions.

Medieval Philosophy

After the rise of Christianity, the neo-Platonist philosopher Plotinus (c. 203-270 CE) asks, “What can it be that has brought the souls to forget the father, God, and, though members of the Divine and entirely of that world, to ignore at once themselves and It?” (Ennead V.1.1). Here Plotinus refers to his interpretation of Plato’s highest principle—The One, or The Good—with the particularly Christian-sounding terms, “Father,” and “God” (Ennead V.1.1). Plotinus’ greatest influence, the middle-Platonist Numenius of Apamea (c. 150-200 CE), created a new school of Platonism with the explicit purpose of demonstrating the overlap between Platonism and ancient near-Eastern religions, like Judaism (which he mentions by name). Indeed, he was the author of the much-quoted saying, “What else is Plato than a Moses who speaks Greek?” (Guthrie 1917, 2). And Plotinus, probably the most famous neo-Platonist in antiquity, saw Platonism not as a merely theoretical study, but as a spiritual path. He describes his own mystical experiences, inspired by Plato’s teachings:

Many times it has happened: lifted out of the body into myself; becoming external to all other things and self-centered; beholding a marvelous beauty; then, more-than ever, assured of community with the loftiest order; enacting the noblest life, acquiring identity with the divine…. (Ennead IV.8.1)

At points he even gives guidance on how to achieve such mystical states, drawn from Plato’s writings, and referring again to God as “Father”:

The Fatherland to us is There whence we have come, and There is The Father. What then is our course, what the manner of our flight? … all this order of things you must set aside and refuse to see: you must close the eyes and call instead upon another vision which is to be waked within you, a vision, the birth-right of all, which few turn to use. (Ennead I.6.8)

This again shows us that in antiquity, what was called “philosophy” was not simply the modern-day concept of a kind of deep, critical thinking about important subjects, but was instead an attempt at what might be called a kind of “spiritual science.” A spiritual path supported by a deep theoretical underpinning, but more than merely theoretical.

In this light, it makes much more sense that early Christians were often critical of “philosophy” (by which they meant Platonism), even when they were themselves engaged in something that—in today’s terms—we would call “philosophy.” They were opposed to it, not because they were opposed to critical thinking, but because Christianity and “philosophy” (i.e., Platonism) essentially constituted rival schools of spirituality, with teachings about the spiritual path that, while frequently overlapping, were often at odds. Indeed, Porphyry (c. 234-305 CE), Plotinus’ star pupil, saw Christianity (as well as Gnosticism) not as something simply unrelated to “philosophy,” but as schools of thought competing with “philosophy” and posing a major threat to Platonism–so much of a threat, in fact, that he wrote a 15-volume work Against the Christians to attack it! Later Platonists (like Iamblichus, c. 245-325 CE) took a different approach and began incorporating aspects of theurgy (a kind of ritualistic “white magic”) into their philosophical systems partly in an effort to compete with popular Christian rituals and liturgical (worship) practices.

After the emperor Justinian discontinued public funding for pagan schools of philosophy in 529 CE, those schools began to fade out for lack of financial support, although classical learning itself was kept alive by Christian scholars in the (Eastern) Roman Empire (usually erroneously referred to as the “Byzantine” Empire) for the next thousand years.^[1] From the Christianization of the Roman Empire until its fall in 1453, most philosophical thinking was done in the context of theological thinking, whether by Greek-speaking Christians,^[2] Latin-speaking Christians,^[3] Muslims,^[4] or Jews.^[5] Although such thinkers gave intense scrutiny to many philosophical questions, they always did so with one eye toward the religious or theological implications of those philosophical questions.

Modern Philosophy

After the armies of the Fourth Crusade sacked the Eastern Christian city of New Rome/Constantinople in the 1200s and brought back precious ancient manuscripts, Western Europe saw the Renaissance blossom in the following century (1300s). After the eventual fall of Constantinople in 1453 (which led many Greek scholars to flee west and bring more knowledge and manuscripts with them), the arrival of Europeans in the Americas in 1492, the rise of Protestantism beginning in 1517, and the Scientific Revolution (perhaps datable to Copernicus’ publication of On the Revolutions of the Heavenly Spheres in 1543), we come to the Modern Period. The rapid pace of discovery of new knowledge and the overturning or questioning of previously-held beliefs from the mid-1400s to mid-1500s led to a period in which Classical learning began to be questioned, doubted, and interrogated to a growing degree. Not surprisingly, and despite being in many ways revolutionary compared to Ancient and Medieval thought, Early Modern Philosophy was still deeply concerned with religious questions.

The philosophies of the great Rationalists—René Descartes (1596-1650), Baruch Spinoza (1632-1677), and Gottfried Wilhelm Leibniz (1646-1716)—were all bound up in many ways with their respective Catholic, Jewish, and Protestant theologies. Descartes’ famous Meditations are largely concerned with proving the existence of God and the distinction of the body and soul. Spinoza’s Ethics argues for his version of pantheism. Leibniz wrote versions of both the Cosmological and Ontological arguments.

Turning from the Rationalists to the British Empiricists, John Locke (1632-1704) was a deeply religious man and authored arguments for God’s existence. Even his political philosophy begins from the premise that we are all God’s property (which he seems to have meant quite seriously), for example, in the Second Treatise on Government 2.6 (Locke [1689] 1980, 9). George Berkeley (1685-1753) was actually a bishop in the Church of England, and a key aspect of his philosophy of “idealism” was the idea that, since matter doesn’t really exist, only minds and ideas do, there has to be one very powerful mind (God) that constantly perceives all things and holds them in existence. Last, among the three great British Empiricists, only David Hume (1711-1776) could reasonably be called an atheist, though this label was more of an accusation by his opponents. His views on religion have been more accurately described as “attenuated deism.” In other words, he seems to have held something like the belief that there is some kind of Creator, who may possibly be something like a Great Mind, but who is not likely to be directly concerned about anything that happens in the world, at least as far as anyone would have any way of knowing (Gaskin 1987, 223 ff.).

Immanuel Kant (1724-1804), whose “critical” philosophy was largely a response to Hume’s skepticism, described his project in The Critique of Pure Reason (B xxxi) as a way to “deny knowledge, in order to make room for faith” (Kant [1781] 1998, 117). While the philosophy of Hegel (1770-1831) is today often summarized in the triadic phrase, “thesis-antithesis-synthesis,” Hegel’s own conceptualization of his philosophy had much more to do with the Christian doctrine of the Trinity (as he interpreted it), which he explicitly stated he was trying to revive, since the theologians of his day had, in his view, abandoned it (Schlitt 2012; Schlitt 2016).^[6]

Finally, although there had been atheist philosophers before, it is only really in the 1800s, with Karl Marx (1818-1883) and Friedrich Nietzsche (1844-1900), that atheistic philosophies begin to gain what will turn out to be a more solid and lasting foothold in the intellectual history of the West. But of course, it would be completely wrong to say that Marx or Nietzsche were not concerned with religious questions. Rather, they were both deeply concerned with questions about religion—they simply came down on the negative side of those questions.

We stand now at an interesting point in history. We saw a decline in religious belief among philosophers beginning in the 1800s but are seeing something of a resurgence today. Is the long interconnection between philosophy and religion from antiquity to the late Modern period an historical accident? Or is it the result of a deep, natural affinity between the two? Does the decline of religious belief among philosophers from the 1800s to the 1900s mean that philosophy finally managed to rid itself of an irrational relic of a bygone age, and will the recent resurgence of the philosophy of religion turn out to be nothing but a blip on the radar? Or will the prevalence of atheism for a century or so turn out to have been the blip on the radar, which we are now seeing the end of? History has yet to yield a final verdict.