Ancient Greek philosophers have much to say about God or the gods; some of them also have much to say about being (whether being as predication or identity, expressed by “X is Y,” or being as existence, expressed by a bare “X is” or “there is an X”). They do not systematically connect the two topics, however, and neither do many modern philosophers. But many medieval philosophers did. Can thinking about being help us understand God? Can thinking about God help us understand being? I will explore some connections that medieval philosophers saw between the two topics, and also some difficulties that they encountered. I will focus not so much on particular philosophers as on central ideas that many different philosophers took up, illustrating these ideas from the work of philosophers who set them out in especially interesting or accessible ways, and noting challenges that different philosophers answered in different ways. Many of these ideas and challenges begin with Muslim authors and are then taken up by Christian authors from the thirteenth century on. I will go back and forth between Muslim and Christian sources.

PHYSICAL AND METAPHYSICAL PROOFS OF GOD

The proofs of the existence of God are an obvious place to begin. Thomas Aquinas, in Summa theologiae I, q. 2, a. 3, says that God’s existence can be proved in five ways. Thomas’s first way, arguing from causes of motion, and his second, from efficient causes, are physical arguments, taken from Aristotle; his fifth way, from teleology, is equally physical, derived ultimately from the Stoics.

The Discourse and Its Genre

When Descartes' mathematics, and what was true in his physics, were surpassed, and what was false in his physics was refuted and ridiculed, the two main works that survived the wreck, and continue to shape our picture of the man, were the Discourse on the Method and the Meditations. Of these, the Meditations is less personal. The Meditator of the Meditations is not specifically René Descartes. Rather he, or she, is a role that any of us can fill if we choose to pursue this path of thinking. By contrast, the Discourse presents to us the life and aims and undertakings, not precisely of René Descartes – for the original 1637 publication was anonymous – but at any rate of the person who is the author of the Essays that the Discourse introduces (the Geometry, the Dioptrics, and the Meteors), who has made many new discoveries through a special method of “searching for truth in the sciences” and who is also the author of some more mysterious treatises that he has chosen not to publish. The Discourse presents this impressive but anonymous person as having made an almost-complete break with the traditional disciplines in which he was educated; he begins his own intellectual work, when he does begin it, not from the lessons of his teachers or from books or from what he learned by travelling in “the book of the world,” but from his own private reflections that lead him to the method described in Part Two.

The seventeenth century saw the emergence of the corpuscularian, or ‘mechanical’, philosophy, which succeeded far beyond any previous science or philosophy in explaining particular phenomena of nature, and which, as a general framework for thought about the physical world, has continued to guide philosophical and scientific investigation down to the present day. Modern scholars have often sought to understand the emergence of this new philosophy by placing it within the context of some previous tradition of thought. In the words of J. H. Randall:

Two generations later, there is still no agreement. In what follows I will not attempt to assess the relative importance of the different intellectual traditions leading up to the seventeenth century (in any case, the relative importance of these different traditions as background will vary widely, depending on which seventeenth-century figure we wish to study), but I will try to indicate the broad range of intellectual traditions in terms of which the various seventeenth-century figures defined their attempts to establish a new philosophy.

Descartes stands at a turning-point in the history of philosophy. The old philosophy of Aristotle had lost its credibility, and the new philosophies of the Renaissance, planned to replace it, turned out to be dead ends. It was Descartes, with such contemporaries as Hobbes and Gassendi, who staked out the road leading, past many further twists and forks, to the philosophy and science of today.

In these circumstances it is natural for modern philosophers to turn back to look at Descartes. Much good interpretive work has been done, and often it has been concerned to compare Descartes' philosophy with the philosophies of his contemporaries and predecessors. Especially in France, which has devoted itself most intensely to the study of its national hero, scholars have investigated the continuity or discontinuity of Descartes' thought with earlier philosophy, particularly in the scholastic and Augustinian traditions. By setting Descartes' thought in relation to these earlier traditions, these scholars have tried to clarify the origin and nature of modern philosophy as such, and of its complicated relations to science and to religion. Both because of his historical importance and because of his intrinsic merit, Descartes is an ideal case study for anyone who wishes to assess the extent of constancy and change, of harmony and disharmony in the history of philosophy; for anyone who wishes to see how far an old philosophy can survive and how much it can contribute in a new scientific or religious setting; and for anyone who wishes to draw a moral for the present and future of traditional philosophy.

True and false wisdom

We now have a reasonable reconstruction of what Augustine found in the “books of the Platonists”; this is the right way into interpreting Augustine's understanding of God and the soul, since (as Augustine tells us in Confessions VII) he reached this understanding by reading and meditating on the books of the Platonists. Turning now from the Platonists to Augustine himself, we can see how he uses the intellectual material of Platonism to work out an understanding of God and other things, compatible with Christianity and explicating the intellectual content of the Christian scriptures. Following Henry's rules of method, our primary evidence must be “Augustine's own testimonies on the writings of the philosophers which he has read, on the circumstances in which he read them, on the intellectual or moral profit which he drew from them, and on the impressions with which they left him.” Augustine testifies explicitly and systematically to his reading of the books of the Platonists in Confessions VII, and only there; so this book, with some supporting material, will provide our point of departure. Once we have learned from Augustine himself what intellectual profit he drew from Platonism, and how he applied it to his Christian intellectual project, we can turn to the treatises and dialogues where he tries to carry out this project, and observe how he actually does what, in the Confessions, he says he is doing.

Augustine and the Platonists

To understand Augustinianism, we must read Augustine's written work as the product of a search for wisdom. The desire for wisdom is constant throughout Augustine's life; he tries different means, and in the end he thinks he has succeeded in part, but only in part. Augustine will transmit to later thinkers both the ideal of wisdom and the means that he has discovered or adapted from earlier sources, whether Christian authorities or Platonic philosophers, for achieving this end. We can best understand Augustinian wisdom by focussing both on his Confessions, describing his search for wisdom, and on those texts, especially the early dialogues culminating in the De Libero Arbitrio, in which he tries to communicate the wisdom that he discovered, both in the Platonists and in Christianity, in the annus mirabilis 386. The Confessions and these early dialogues give consistent and mutually illuminating accounts of Augustine's discovery; undeniably, though, Augustine's thought develops after 386 (both before and after the writing of the Confessions around 397), and we will discuss later changes where they are relevant to the Augustinianisms of later thinkers, including Descartes.

The Confessions is about wisdom. It is misleading to think of the book as describing Augustine's conversion to Christianity: conversio is indeed a central theme, but for Augustine this word means, not a change of religious allegiance, but a turning toward God and away from other things.

Isolating the rational soul

The second and third Meditations belong together as Descartes' attempt to prove the positive part of the Meditations' general thesis that God and the soul are the best known of all things, and are therefore the appropriate principles of philosophy. Descartes had argued in the first Meditation that we cannot know bodies without first knowing God and the soul; he now attempts to show that we can have some knowledge of God and the soul without making any assumptions about bodies. The second Meditation is actually entitled “of the nature of the human mind, that it is better known than the body,” and the third Meditation makes the same claim about God.

In both the second and the third Meditations, Descartes is adapting the line of thought that Augustine uses, in Confessions VII and De Libero Arbitrio II and elsewhere, to bring us to knowledge, first of the soul, and then of God. Descartes' differences from Augustine arise from his attempt to show that the cognitiones of soul and God are the first, that is, both that these are independent of all other knowledge, and that no other cognitiones are similarly independent. Although the Confessions simply narrate an intellectual “vision” of God, in the De Libero Arbitrio Augustine tries to prove to Evodius that God exists, starting from Evodius' acknowledgment that he himself exists.

The question of Descartes and Augustine is an old one, but it has never been answered satisfactorily, and it seems not to have been studied seriously for more than half a century. My work picks up from studies of Gilson and Gouhier dating mostly from the 1920s; and while I disagree with many of their conclusions, I do so with deep respect for their pioneering work, and I will be happy if this book has the effect of directing scholars' attention back to a line of inquiry that was too soon abandoned.

It may help to explain two things that this book is not. First, although I have already seen my title misstated in print as “Descartes and Augustinianism,” the book is not a study of Descartes and seventeenth-century Augustinians, or an attempt to relate Descartes to the Augustinian tradition. I am not sure there was an Augustinian tradition: this phrase suggests a series of thinkers reading Augustine through their predecessors, and distinguished by some common doctrine from thinkers outside the school. There was, in that sense, an Aristotelian tradition. But the history of Augustinianism is the history of the many revivals of Augustine by different thinkers, who have each discovered some new aspect of Augustine's thought, and seen in it a way to answer the philosophical or theological challenges of their own times.

The creation of the eternal truths

Descartes has argued that we can establish a science of bodies only if we first secure an independent knowledge of the soul, and establish a criterion of its cognitive faculties; and he has argued that we can establish such a criterion only through knowing God as Nous. This knowledge of soul and God may be a necessary condition for science; but is it also sufficient? Descartes, like Plotinus and Augustine, conceives God as the source of knowledge to the soul; like Plotinus and Augustine, he uses this conception to lead us up to God; but unlike Plotinus and Augustine, he is equally interested in leading us back down. The fourth Meditation already is looking for “a way … from the contemplation of the true God … to the knowledge of other things” (AT VII, 53), without specifying which “other things” these are; the fifth and sixth Meditations turn specifically to derive knowledge of the essence and existence of bodies, and Part Two of the Principles claims to derive the “principles of material things” from the metaphysical principles of Part One. In the present chapter, without discussing Descartes' physics in detail, I will describe Descartes' strategy for arguing from metaphysics to physics, to the extent that this affects the meaning of his metaphysics and of his philosophical project as a whole.