One of my favorite tasks as a theological librarian at Drew University is orienting new seminarians to the theological reference room, which sits apart in isolated splendor from the rest of the library. Perhaps housing theology books in their own room is meant to illustrate the concept of sanctity, which in its original Hebrew simply meant separate.

Because of recent space limitations in the library, some philosophy books, which began to overflow their shelves, have infiltrated the theological reference room. They bunch together at one end of the room in free-standing shelves, not like the religion books, which snugly hug the walls. I like warning the students to beware of philosophical intruders like Nietzsche, Heidegger, and Kierkegaard, because many were hostile to the seminarian’s chosen profession. And though my warning brings a chuckle, it carries a grain of truth. For philosophical reason, even at its most virulently antirational, seems to inhibit those elements of the mind that must be engaged if spirituality is to flourish.

I explore this topic in a class I teach at the New School University in New York. The class, called Philosophical Spirituality, examines the potential of philosophy, apart from religion, to nurture spiritual life. This holds special interest in a cultural climate like ours, which differentiates spirituality from religion. Religionless spirituality is often criticized for lacking the depth of a grounding tradition. The ancient traditions often marshaled in support of free-floating spirituality-whether Native American, Kabbalistic, or Hindu-lose authenticity, so the critique goes, when they are uncritically adapted to what are often middle-class American lifestyles. The goal of my class is to uncover in Western philosophy a religionless spirituality that already constitutes a tradition of its own.

Part of what commends such a spirituality to modern readers is its therapeutic dimension, its concern with human happiness. That philosophy is therapy is a very old idea now undergoing a revival, stimulated, unexpectedly, by voices within the academy. Scholars of Hellenistic philosophy, such as Martha Nussbaum and Pierre Hadot, have spearheaded this revival. For it is precisely the ancient Stoics and Epicureans, long dismissed in academic survey courses of philosophy for lacking intellectual originality, who shifted to center stage the therapeutic import of philosophy. Both Nussbaum, in her book The Therapy of Desire, and Hadot, in his Philosophy as a Way of Life, uncover for modern readers how much ancient philosophy was a psychologically nuanced healing practice (rather than a mere intellectual exercise), and one that Hadot, especially, suggests remains to this day what William James would call, a “live option.”

And so it is not surprising that, first in Europe, and now here, a new vocation for professional philosophers has evolved. The recently founded American Philosophical Practitioners Association is a professional organization whose members, according to its Web site, “apply philosophical systems, insights, and methods to the management of human problems and the amelioration of human estates.” But there are more popular expressions of therapeutic philosophy. The School of Practical Philosophy in New York advertises its services on a subway poster, which displays a melancholy fish enclosed in a bowl who finds freedom and happiness in the open sea by the wonders of philosophy. As the poster boldly claims, “Philosophy Works.” There is even a line of beauty products, called Philosophy, which promises its users will “love, without expectation, all people.”

Philosophy as therapy is already halfway to philosophy as spirituality. A philosophical therapy that grounds the happiness it promises in a sense of the sacred, understood most broadly as the source of all being and well-being, becomes a spirituality. If something as old as philosophical therapy can enjoy a modern revival, then philosophical spirituality, too, may be ripe for revival.

The idea itself has its challenges-for example, the term philosophical tradition is already a paradox. Philosophy claims that it does not simply accept on authority what has been handed down from the past. It understands itself to maintain an ongoing openness to new beginnings. A later philosopher typically agrees with an earlier one on the basis of reasoning or experience they share, not any unquestionable superiority the earlier enjoys. My hope is that by having my students examine a sequence of philosophers-Ecclesiastes, Plato, Lucretius, Marcus Aurelius, Descartes, Spinoza, Kant, Hegel, Novalis, Kierkegaard, Emerson, William James, Bertrand Russell, Simone Weil-they will, through the sheer juxtaposition of thought systems, see the philosophers’ common spiritual core.

In the first class meeting, I distribute a working outline of what that core might be. Philosophical spirituality endorses a belief that reality can and does accommodate human happiness; that this happiness derives from proximity to the sacred; and that natural human reason and experience suffice to bring us there. Contrasting this with some aspects of Western religion, I note that philosophical spirituality values questions over answers, universals over particulars, and individual self-sufficiency over community relations; and that its belief in the afterlife, if it has one, is a reasoned defense of immortality. It is a tall order to expect the philosophers in the syllabus to illustrate these characteristics, and not all of them do. But even where they don’t, there are lessons to be learned.

I begin the presentation of each philosopher with a brief discussion of his or her inherited religion and critical rejection of it. For Plato, I cite his critique of Homer; for Spinoza, his critique of Torah; for Kant, his critique of Lutheran pietism. I lay the foundation for this contrast in the first session, where I divide the blackboard in half, religion on one side, philosophy on the other. Religion, I say, begins in story, which overflows into doctrine, rite, and community; while philosophy, I suggest, quoting Aristotle, begins in wonder, which does not necessarily adopt religious forms. Whereas revelation is the chief channel of religious knowledge, reason, experience, and sometimes imagination compose philosophical knowledge. The hard part is articulating a single concept of spirituality that both philosophy and religion can address. Spirituality, as I present it, is an understanding of a path to the sacred.

Most of the religion-rejecting philosophers we discuss in class are Protestants by culture. There is only one bona fide Catholic: Descartes. Could this mean that philosophical Catholics find enough scope for reason, experience, and imagination in their religion that they do not need to position themselves against it? Jean Leclercq addresses this question in his book on medieval Benedictine spirituality, The Love of Learning and the Desire for God. Leclercq is more concerned with devotional forms of reading and the spiritual significance of literacy than with philosophy as such. Monks sought neither conceptual innovation nor the satisfaction of intellectual curiosity, but rather, “the establishment of a certain contact with God, a profound attachment to him,” Leclercq writes. He argues that by the high Middle Ages, monastic spirituality was in tension with its more purely intellectual and philosophical counterpart, scholasticism.

The scholastics sought conceptual clarity in the interplay of question and answer. Their methods were less grounded in devotional reading than in Greek philosophy. The tension between what Leclercq calls the monastic and the scholastic Middle Ages peaked in the conflict between Bernard of Clairvaux and Peter Abelard over the issue of religion and philosophy. Bernard, a Cistercian monk, opposed philosophy. Abelard was the preeminent philosopher and theologian of his time. That Abelard was known more as the illicit lover of Heloise than as a brilliant logician is a subtle tribute to the erotic undertones of Greek philosophy. Leclercq’s point in replaying the Bernard-vs.-Abelard episode is that up through the end of the Middle Ages, philosophy and spirituality were often (with notable exceptions, for example, Bonaventure) opposed.

There are enough echoes of this idea on either side of the Middle Ages (in the ancient and modern worlds) to seriously challenge and enliven the thesis of my class that there is a philosophical tradition of spirituality. The challenge may come from a religionist critiquing philosophy or from a philosopher dismissing spirituality. Such examples are found in St. Paul and Descartes.

Paul calls philosophy an “empty deceit, according to human tradition” (Col 2:8), of course, yet he may not be as hostile to philosophy as that passage makes him sound. One can interpret him as a practicing philosopher. Such an interpretation was aired last April at a conference at Syracuse University called “St. Paul among the Philosophers: Subjectivity, Universality, and the Event.” How authentic, the conference asked, is the supposed universality of the philosophers, which presumes to rise above all limitations of history, ethnicity, and gender? Not very, is one way to interpret Paul in Col. 2:8, if we take him to mean that philosophy is more constrained by tradition than it realizes. But according to one conference speaker, Daniel Boyarin, of the University of California at Berkeley, Paul was a kind of philosopher. He took that role in order to address the intractable contradictions that confronted him (for example, in his stance toward the Jews, who seemed to Paul both uniquely blessed and superseded). Boyarin argued that the paradoxes in Paul’s captivating rhetorical flourishes had precedent in the ancient philosophical school of the Sophists, who reasoned that ambiguous, self-contradictory language was needed to negotiate the two-sided nature of reality.

Paul didn’t see philosophy as a self-sufficient path to the sacred. It had its uses, but none was spiritual. For purposes of my class, Paul is the perfect counterweight to philosophical spirituality on one key point: the afterlife. For about one thing Paul is not at all ambiguous: “if Christ has not been raised, your faith is futile” (1 Cor. 15:17). By professing belief in bodily resurrection, Paul differentiated himself from the older Pythagorean and Platonic views that what survives our death is an immortal soul. What further distances Paul from philosophy is that his belief in resurrection rests not on the sort of reasoned argument Plato gave for immortality, but on extraordinary supernatural experience: the dramatic intrusion of the risen Christ into his life. On this point, according to Acts 17, Paul addresses the philosophers of Athens, the Epicureans and Stoics, who doubted there was an afterlife at all, and he was “mocked.”

Oddly, Acts 17 identifies Stoics and Epicureans in Paul’s audience, but not the Platonists. Why are they not mentioned? Their absence invites one to superimpose their presence and imagine the result. I envision the Platonists, who shared Paul’s belief in an afterlife, listening to Paul with bemused curiosity. Plato was not above sophistry himself, much as his Socrates derides that competing philosophical school. After all, Plato’s attitude toward the body is contradictory across his many dialogues. On one hand, Plato views the body as the prison of the soul; but on the other, it is the memory of a higher beauty the soul knew in a preborn state, which transports it back to the time of its preborn life. A beautiful, resurrected body would be a curiosity for the Platonists, but a redundant one, since in the afterlife the wisest souls know fully the surpassing beauty of the world of ideas. So I think the Platonists would not have mocked, but merely turned away from Paul’s curious but ultimately redundant idea of resurrection.

Why then are they excluded from Acts 17? The deeper problem for the writer of Acts is that Platonism is too tempting an alternative to Paul to be admitted to the story. Yet this has always been true for many Christians. For example, Leclercq offers a picture of an industrious monk working faithfully to copy the text of a church father while cherishing Plato in his soul. The writer of Acts betrays his anti-Platonic hand when he has Paul comment on the inscription to an “Unknown God” (Acts 17:23). For while the author of that inscription might simply have been ignorant of which Greek gods he was obliged to thank, the term also evokes Plato’s idea that the nearer we come to the sacred, the less we can describe it.

Such a paradoxically unknowing knowledge of the sacred isn’t found only in Plato. It is a reigning idea in some of the medieval Christian mystics, such as Nicholas of Cusa (1401-1464), who wrote the De docta ignorantia on just this subject. In his book, Christian Spirituality, French scholar Pierre Pourrat observes that “it was Platonic philosophy that served, first of all, as a basis for mystical speculation.” This is significant because it uncovers the attraction of Plato for some Christians. It becomes all the more important, then, to differentiate Platonic spirituality from its Christian cousin. Pourrat chooses his words carefully. Plato was the basis (not the completion) for mystical speculation (not experience). By contrast, within philosophical spirituality, Plato supplies both basis for and completion of, speculation on and experience of, the realm of the sacred. How can this be?

I first encountered Plato in high school. I couldn’t understand the fuss that was made over him. I read him again in various contexts throughout college and graduate school, but only came to understand the devotional approach to him much later in life, when I participated in a series of adult-education seminars offered by the University of Chicago, a four-year great-books program. Divided as we were in the class between realists and idealists, we all warmed to Plato’s skills as a playwright. We saw how his dialogues often opened onto an abstract question from the entrée of some engaging human drama, like a trial, or a banquet, with which we could all identify. We learned to discern in the dramatic prelude an anchor in human life for the ideas to come. For example, in the playful conflict of wills that opens the Republic, over whether Socrates will abide with his friends or not, we saw Plato foretell the impending abstract question of whether justice is the power of the stronger.

Two key passages in the dialogues especially moved me: the famous description of the ascent from the cave in the Republic, and the less well-known account of the soul sprouting wings in the Phaedrus. Images of ascent and wings have immediate appeal to anyone who has ever been fascinated by angels (or birds). That both passages take the form of a story also helps explain their appeal.

Socrates must speak in story form, he explains to his interlocutors, because what he wants to describe exceeds the reach of reasoned language. Rather than describe his subject, Plato wants to position his readers to experience the realm of the sacred, the Idea of the Good. Philosophy’s words are the means of travel to the Good, not the journey’s end point. What makes Plato a spiritual writer is that he is able to evoke for his readers the place of the sacred and, simultaneously with the evocation, he appears to take them there. What makes his spirituality philosophical is that it comes by way of humanly penned, reasoned, and imaginative words.

Now for the modern challenge to philosophical spirituality: Descartes. At first, he was not even part of my class syllabus. I added him only because it was so difficult to understand the more explicitly spiritual Spinoza apart from him. Descartes is a cornucopia of paradox. Philosopher Amélie Rorty wisely warns us of “his usual confident and engaging obscurity.” Descartes’s philosophy hovers suspended between a string of opposites: theory and practice, nature and reason, self-sufficiency and interdependence, conjecture and certainty, innovation and tradition, French and Latin, dream and reality, and, most important for me, science and spirituality. Like his contemporary Pascal, he was a scientist (mathematician). Descartes’s philosophy derives from the same medieval scholasticism that Jean Leclercq described as opposed to spirituality. It’s as though when seventeenth-century French philosophy raised its head above its scholastic confines and looked out onto the wide spaces opening up around it, it saw two chief figures on the horizon: natural science and the Catholic Church. It had to choose which to ally itself with. Pascal chose the church. The fascination of Descartes is that he is confidently obscure about which he chose.

As religious studies scholar James M. Byrne observes, Pascal never forgave Descartes for proving the existence of a God whose only use to philosophy was to guarantee the existence of the external world. This is the main function of God in the Meditations. Descartes proves God by a version of the old ontological argument, that from the sheer idea of God, if properly thought, his existence necessarily follows. This would seem a momentous demonstration in its own right. But Descartes does not stop there. He subordinates the God he has proved to the role of silencing those skeptical of the world’s existence at all. For the good God would never lure us with false impressions into believing a world that appears to exist but really does not. If the reality of the external world is the true quest of Descartes’s philosophy, that is because he wants, as he tells us at the beginning of the Meditations, to lay the groundwork for science. The sciences do not even commence if we can’t be sure the world they describe exists.

So Descartes makes the scientists happy. But what does he do for the spiritually inclined? The world God guarantees turns out to be particularly austere. It is a mechanism devoid of color (which is indeed, it turns out, an illusion of our senses), and exhaustively describable in terms of mathematical formulas. In The Passions of the Soul, Descartes suggests that the greatest happiness comes from the unimpeded exercise of intellect. In light of that argument, one must wonder whether the pleasure Descartes has in his proof of God’s existence is in the God he has proved or in the power of his own ability to prove it.

And yet, at the end of the third meditation, where Descartes proves God, he pauses. Descartes interrupts the flow of his reasoning to contemplate the God he has just proved, for this, he says, is our highest happiness. A God reached by the sheer exercise of thought who supplies our greatest happiness-this is the language of philosophical spirituality. It is difficult to believe that Descartes includes this contemplative interlude-embedded so far into his book (at midpoint)-simply to please his powerful Catholic readers. Indeed, it may not please them to see a philosopher’s God so ardently contemplated. The passage also draws attention to the very title Descartes chose for this book: Meditations. For seventeenth-century readers, as much as for us, this word would connote a spiritual attentiveness or reverie. Some interpreters of Descartes, such as Walter John Stohrer, link the title to the Ignatian retreats he experienced at the Jesuit school he attended as a boy. Both Ignatius’s Spiritual Exercises and Descartes’s Meditations proceed according to cumulative, alternating stages of purgation and illumination; both require the strenuous exercise of reason; both work best in remove from the world (on retreat). The Meditations becomes a spiritual exercise in quest of certain knowledge of God. Truth is the equivalent of goodness, error of sin, and the idea of God, the equivalent of God.

Almost alone among the philosophers in my class syllabus, Descartes speaks respectfully of his inherited religion, Catholicism. As with so much else in Descartes, this respect invites precisely opposite interpretations, either as sincere tribute to his native faith or as politically motivated caution (Spinoza’s motto) in the age of Galileo. There is a simple way to resolve the seeming tension in Descartes between the science he serves and the spirituality he inserts in his work. Perhaps he was less a spiritual philosopher than a Catholic one, whose spirituality was adequately served by his faith, and so he did not seek the channel of philosophy.

There are three contexts for which Descartes explicitly endorses religious over philosophical spirituality: when we are working through our philosophy and have not yet derived its practical implications for our life; when we are not philosophical at all; and when we are trying to console a friend who has lost a loved one. This last context materialized in my class. One student lost a friend to the war in Iraq. Perhaps the most memorable comment on the reading assignments came from him, when he observed that the problem with philosophy is that it fails fully to console. If he is right, I must not only reconsider whether Descartes belongs in the syllabus, but whether “philosophy works” at all.