Modern philosophy is usually taken to date from the seventeenth century, and René Descartes (1596–1650) is often named as its father. This need not mean that Descartes was the first noteworthy and identifiably ‘modern’ philosopher. Thomas Hobbes (1588– 1679) has claims there too. What it does mean is that Descartes more than others was responsible for the style, the shape, and the content of much subsequent philosophy—at first on the Continent, and then in England.1 His distinction between extended and thinking substance, his proofs of his own existence and of that of a good God, his account of the material world as one of extended matter in motion, all stirred up controversy and discussion whose waves rocked the remainder of the seventeenth century and troubled most of the eighteenth, and whose ripples are still discernible today. Contemporary reports, from both sides of the English Channel, testify to one aspect of his importance: his freshness and newness. According to Christian Huygens, the Dutch mathematician, astronomer, and physicist,
What greatly pleased in the beginning when this philosophy began to appear is that one understood what M. des Cartes was saying, while the other philosophers gave us words that made nothing comprehensible, such as qualities, substantial forms, intentional species, etc. He rejected more universally than any other before him this irrelevant paraphernalia. But what especially recommended his philosophy, is that he did not stop short at giving a disgust for the old, but he dared to substitute causes that can be understood of all there is in nature.
(trans. Dugas 1958:312)
It was to the same ‘justly-admired gentleman’ that John Locke said he owed ‘the great obligation of my first deliverance from the unintelligible way of talking of the philosophy in use in the schools in his time’ (1823:4.48).
In these testimonials to Descartes’s influence on the seventeenth century his ‘new’ philosophy is contrasted with an ‘official’, Scholastic, or ‘school’ philosophy—a philosophy filled with ideas which had begun to seem unintelligible. This older philosophy belongs to a broadly Aristotelian tradition, and it is the explicit rejection of this tradition, and of the authority of Aristotle, that marks for Descartes, and for many of his contemporaries and successors, their own sense of their ‘modernity’.
Two people for whom Descartes’s philosophy set a new, post- Aristotelian scene were Benedict Spinoza (1632–77) and Gottfried Leibniz (1646–1716). Leibniz says that Spinoza ‘only cultivated certain seeds in the philosophy of Descartes’ (G 2.563) and that his philosophy is ‘an exaggerated Cartesianism’ (T 359). As for Descartes himself, he is someone ‘whose genius is elevated almost above all praise’. He ‘certainly began the true and right way’, and said ‘excellent and original things’. Yet Leibniz’s praise had its limits: though going so far as to be ‘the entrance hall to the truth’, Descartes’s philosophy ‘missed the mark’ and did not quite make it.2 Leibniz’s disagreements with it are deep. Spinoza too had his criticisms of Descartes,3 and Descartes’s own followers were keen, on theological grounds, to dispel any idea that Spinoza might be one of them.4 None of this, however, prevented the development of a tradition which pictures both Spinoza and Leibniz as ‘Cartesians’.5 In its discussion of the metaphysical views of these three important seventeenth-century philosophers this book supposes that there are intrinsic relations between them. But it formulates no general conclusions about whether Spinoza and Leibniz are or are not ‘Cartesians’. It simply proceeds on the assumption—an assumption to be judged by its fruits—that the very shape or conceptual content, and not the mere verbal dress,6 of many of Spinoza’s ideas have Cartesian ones as a background; and that (whether directly, or indirectly via Spinoza) the same is true of Leibniz.
Spinoza was 18 when Descartes died, and they neither met nor corresponded. In 1663, however, he published an exposition of Descartes’s influential Principles of Philosophy (1644). This wasdesigned as tuition material for a pupil to whom, Spinoza says, ‘I did not want to teach my own opinions openly’ (Ep13/C 207), and Spinoza agreed with friends that he should ‘warn…Readers that I did not acknowledge all the opinions…as my own, since I had written many things…which were the very opposite of what I held’ (Ep13/C 207). Nevertheless its very existence betokens a deep understanding of, and concern with, Cartesianism. It is no surprise that Spinoza’s own philosophy in his Ethics (1677) shows keen awareness of Descartes’s.
Fourteen years younger than Spinoza, Leibniz was only 4 when Descartes died. They had quasi-personal contact when Leibniz met Descartes’s friend and literary executor, Claude Clerselier, who showed him some of Descartes’s unpublished papers.7 But like any other European philosopher of the time, Leibniz read and studied Descartes, and in the 1690s he too had plans to publish an assessment of Descartes’s Principles of Philosophy8 This assessment would have brought together all the ways in which Descartes, so near to the truth, had yet ‘missed the mark’ (L 432), and all the criticisms Leibniz had developed over the years, and out of which his own positive views had emerged. His relationship to Descartes is well-summed up in a letter of 1680:
I esteem Mr Descartes almost as much as one can esteem any man, and though there are among his opinions some which seem false to me…this does not keep me from saying that we owe nearly as much to Galileo and to him in philosophical matters as to the whole of antiquity.
As for Spinoza and Leibniz, they both corresponded and met. In 1671, in an exchange of letters on optics,9 Spinoza offered to send Leibniz his recently published Tractatus Theologico-Politicus. Later, in 1675, Leibniz was suggested to Spinoza as someone ‘very expert in metaphysical studies’ (Ep 70/W 339), and hence as someone to whom the manuscript of the Ethics, then circulating among Spinoza’s friends, might usefully be shown. Spinoza, whose Tractatus Theologico-Politicus (1670) had already become infamous, considered ‘it imprudent to entrust my writings to him so soon’ (Ep 72/W 431), and asked that more be learnt about Leibniz’s character. In the event, Leibniz met with Spinoza in Holland the next year and, he reported, ‘spoke with him several times and for very long’ (L 167); according to notes he made at thetime, at least some of the discussion concerned the Ethics. Spinoza died the next year, and when the Ethics was eventually published Leibniz made further detailed notes.10 Many of these are critical, as are most of the comments on Spinoza which are scattered through his writings. Like others at the time Leibniz thought that Spinoza’s ideas were dangerous to religion; his view of the nature of God and creation in particular. He often explicitly contrasts his own doctrines with Spinoza’s. A letter he wrote on the publication of Spinoza’s Ethics gives an assessment of the relationship between their ideas:
I have found there a number of excellent thoughts which agree with my own, as some of my friends know who have also learned from Spinoza. But there are also paradoxes which I do not find true or even plausible. As, for example, that there is only one substance, namely God; that creatures [created things] are modes or accidents of God.… I consider this book dangerous for those who wish to take the pains to master it.
This book discusses the metaphysics of these three philosophers. Specifically, it focuses on what Descartes, Spinoza, and Leibniz say about ‘substance’. ‘[F]ailure to understand the nature’ of this is, says Leibniz, ‘the cause of [Descartes’s] errors’ (L 433) and of Spinoza’s ‘paradoxes’ (L 195). But what is ‘metaphysics’? What is ‘substance’?
The term ‘metaphysics’ originated as the title of some of Aristotle’s books. Though Aristotle himself called the subject matter of these books ‘first philosophy’, it appears that in early editions of his works they were arranged in order after his book Physics; so they, and hence their subject matter, came to be known as Metaphysics (‘after’, ‘above’, or ‘beyond’ the Physics). One part of ‘first philosophy’ as conceived by Aristotle was the study of ‘being as being’ (Met 1003a20), a study which concerns the question what being is. This question, says Aristotle, ‘was raised of old and is raised now and always, and is always the subject of doubt’; and he adds that the question ‘What is being?’ ‘is just the question, what is substance?’ (Met 1028b3). The questions are the same because the Greek for the English word ‘substance’ (Latin: substantia) is ousia, which comes from the Greek verb for ‘to be’. One natural way to understand the question what being or substance is, and one which fits much of what Aristotle says, is as a request for an account of what is real. ‘What does reality comprise?’ (Stead:66), a recent writer on Aristotle puts it. So, as Aristotle remarks, ‘substance’ or ‘being’ is ‘thought to belong most obviously to bodies’ (Met 1028b9); these are what are most naturally picked out as constitutive of reality. ‘[W]e say that not only animals and plants…are substances, but also natural bodies such as fire and water and earth.’ But whether this initial, ‘most obvious’, thought is right, whether these really are substances, is, says Aristotle, something which ‘must be considered’ (Met 1028b8–16).
To a considerable extent Aristotle thinks the thought is correct, though on the way to this conclusion he gives a lengthy account of just what it is about animals, plants, and natural bodies that constitutes their being or substantiality. Moreover, as he points out, some people have thought otherwise. Various earlier Greek philosophers had thought that reality consists ultimately in something other than these things, something of which these things are merely the surface phenomena. Some had held that there is one basic substance or ultimately real being: according to Thales this is ‘water’; according to Parmenides it is an everlasting, motionless, and homogeneous ‘One’. Some had held that there is more than one basic substance or ultimately real being: according to Empedocles the world as we know it is produced from four ‘roots’ or ‘elements’—Fire, Air, Earth, Water—worked on by the two principles of Love and Strife; according to the atomists such as Democritus it is a result of the chance movements and collisions of differently shaped indivisible atoms.
The ancient Greek interest in metaphysics, and its core question about substance or being, is shared by the philosophers of the seventeenth century. In fact it is one of their central concerns. According to Leibniz, ‘the consideration of substance is of the greatest importance and fruitfulness for philosophy’ (NE 151); and these words could serve as a motto not only for his work but also for that of Descartes and Spinoza. He also says, in an article ‘On the correction of metaphysics and the concept of substance’, that unlike Descartes’s account, which led to error, his ‘is so fruitful that there follow from it primary truths, even about God and minds and the nature of bodies—truths heretofore known in part though barely demonstrated, and unknown in part, but ofthe greatest utility for the future in the other sciences’ (L 433). Leibniz’s estimation of the importance of the concept of substance is correct. What he says follows from his account is the heart of nearly the whole of his philosophy; and Spinoza’s great work, the Ethics, is essentially nothing less than a lengthy elaboration of the definition of substance with which it all but opens. As for Descartes, though his writings are not so clearly structured as a metaphysics of substance, he certainly develops one at length, and many of his philosophical views connect with it; without it, Spinoza and Leibniz would not have written as they did.
Besides sharing an interest in the question what substance or being is, the philosophers of the seventeenth century also retain the original Aristotelian idea of metaphysics as ‘first’ or foundational philosophy. This is vividly presented in the preface to Descartes’s Principles of Philosophy, where the whole of philosophy is portrayed as a tree: ‘The roots are metaphysics, the trunk is physics, and the branches emerging from the trunk are all the other sciences’ (CSM 1.186). The idea of metaphysics—‘this regal science’ (L 432)—as the foundation or source of other branches of knowledge is taken up by Leibniz too. Sciences such as physics depend on it: ‘the laws of mechanics…flow…from metaphysical principles’ (trans. MacDonald Ross:146); they ‘cannot be advanced without metaphysical principles’, principles without which ‘general physics is entirely incomplete’ (trans. MacDonald Ross:154).
Given the actual origin of the term ‘metaphysics’, it is just a coincidence that a main concern of ‘first philosophy’, as understood and developed not only by Aristotle but also in the seventeenth century, can be thought of as metaphysical or beyond physics in the sense of being more basic, abstract and general than physics. Physics, we might say, tells us about the details of the world’s phenomena; metaphysics about what underlies those phenomena, what the reality, being, or substantiality of the world basically or ultimately consists in. Thus, to understand the detailed workings of the world, all the phenomena and appearances which it presents to us, is to understand them in terms of the properties and activities of the substances which constitute the world. But, in the context of the philosophy of the seventeenth century, it is a particularly nice coincidence. That century saw the emergence and development of what we now know as modern science. It saw the publication of Johannes Kepler’s New Astronomyor Celestial Physics (1609), William Harvey’s Anatomical Essay on the Motion of the Heart and Blood (1628), Galileo Galilei’s Dialogues on the Two Chief Systems of the World (1632), and Isaac Newton’s The Mathematical Principles of Natural Philosophy (1687). It saw the development of the telescope and the microscope. It saw the foundation of scientific societies such as the Royal Society of London for the Advancement of Experimental Knowledge (1660s); and it saw the work of occupants of the ‘Hall of Scientific Fame’, such as Robert Boyle, Robert Hooke, and Christian Huygens. Later chapters of this book will show how the metaphysics of Descartes, Spinoza, and Leibniz not only provide general background conceptions of the world as described in detail by the more particular sciences, but also contribute quite directly to the theoretical foundations of seventeenth-century physics and mechanics.
Even though the rejection of Aristotle marks for the philosophers of the seventeenth century their own sense of their ‘modernity’, they hardly free themselves from the Scholastic tradition completely. Leaving aside the fact that Leibniz even wished to reins...