Gottfried Wilhelm Leibniz 'was born at Leipzig on July 1, 1646 into a noble and academic family, the son of Friedrich Leibniz,' Professor of Moral Philosophy and Registrar of the University of Leipzig, and of Friedrich's third wife, Catharina Schmuck, the daughter of a Professor of Law. Leibniz lost his father in 1652 at the age of six, and his mother took charge of his education. He started school at seven, and, as soon as he knew enough Latin (which, Leibniz says, he taught himself at seven or eight), he was allowed into his father's library. There he undertook a vast reading of poets, orators, historians, jurists, philosophers, mathematicians, and theologians - from Livy and Clavisius to Cicero, Quintilian, Seneca, and Pliny, to Herodotus, Xenophon, and Plato, to the histories of the Roman Empire and the Fathers of the Church. His universal and assiduous reading made him knowledgable in almost every field.

Leibniz's late metaphysics is dominated by his theory of monads, a doctrine that posits that the only fully real beings are unextended, soul-like substances.' Since the seventeenth century, this theory has perplexed Leibniz's readers. Not only is the notion of the monad itself - a substance that is in his description “windowless”and “like a world of its own” - hard to fathom, but it is difficult to see how Leibniz means to integrate the doctrine of monads with a plausible account of the nature of matter and with his famous hypothesis of the preestablished harmony of soul and body.

I begin by looking briefly at the relationship of Leibnizls late metaphysics to his earlier thought from the vantage point of his New System (I), a transitional work that will also serve to introduce us to the issues most central to his later period. Subsequent sections examine the details of the theory of monads (11), his reduction of matter to monads (111), and the status accorded by his late philosophy to the notions of soul-body union and corporeal substance (IV).

Few philosophical theses are so renowned as Leibniz's illustrious claim that this is the best of all possible worlds. Ironically, the doctrine's great fame is due more to the ridicule it received in Candide than to broad public familiarity with Leibniz's ideas. Even among philosophers well acquainted with Leibnizian texts, the subject of God's standards of perfection has only recently begun to receive detailed discussion. Yet these standards are essential to the meaning of the best possible world doctrine, and the place of humanity in the divine scheme is at the heart of Leibniz's treatment of the problem of evil. Consequently, it behooves us to ask what canons God invokes when he compares possible worlds, and in what ways these standards affect the prospects for human well-being.

The Discourse on Metaphysics of 1686 is generally regarded as the first complete presentation of Leibniz's mature metaphysics. In this chapter, we trace the development of that philosophy from Leibniz's youth, through his years in Paris, to his time in Hanover. Because the metaphysics of the 1680s has lately received so much attention and because the importance of the earlier philosophy has generally not been recognized, we concentrate on Leibniz's thought prior to 1680. In section I, we present the intellectual context in which his youthful metaphysics is most easily understood and summarize both his original metaphysical principles and his first conception of substance. We claim that these metaphysical principles, all of which concern substance, form the bedrock of Leibniz's philosophy for years to come. In section 2, we unearth an inconsistency that Leibniz discovered between his first account of substance and the principles, and trace the steps he took in revising the former. In section 3, we argue that this concept of substance, combined with certain theological commitments, led Leibniz to develop most of the central doctrines of his mature thought. For example, we claim that by April, 1676, Leibniz has arrived at his doctrine of preestablished harmony. In section 4, we discuss the relationship between his concept containment theory of truth, which grew out of intensive work on logic in 1679, and his theory of substance. We finally give a brief summary of the central doctrines of the metaphysics of the Discourse.

Leibniz's views on language, and on the relationship of language to philosophy, constitute a rich and, until recently, little explored area of his thought. Unlike some of his seventeenth-century contemporaries, Leibniz was conscious of a deep connection between the human capacity for language and the capacity to comprehend reality. Language is less a barrier between the mind and the world that must so far as possible be overcome than a lens that necessarily intervenes between mind and world and that can, depending on the skill of the optician, either distort or magnify our apprehension of the world. Accordingly, a careful study of language forms an essential part of the method of philosophy.

It is helpful at the outset to distinguish two primary focal points of Leibniz's interest in language. Within his writings these are represented, on the one hand, by the many sketches and plans associated with the notion of an ideal, artificial language - the “universal characteristic”; and, on the other, by numerous historical and philological investigations of natural languages, many of them directed towards uncovering the common roots of a multitude of human languages. On the face of it, there seems to be a tension between the aims and assumptions of these two very different approaches to the subject of language.

Many of the Modern philosophers, most conspicuously Descartes and his followers, seem to have played down their debt to previous philosophy and left little hint as to their background and influences. Leibniz was not in step with this trend towards setting past philosophy aside. He not only regretted the tendency in others but made a practice of locating his own discussions within a broad tradition of philosophical debate. Although he was in his own eyes a Modern philosopher, Leibniz encouraged the revival of the philosophy of the ancients and the selection from it of what was relevant to contemporary problems.' Both in his respect for past philosophers and in his willingness to draw on them in an eclectic manner, Leibniz belonged within the tradition of Renaissance humanism.

Renaissance humanism derived from the fifteenth century but continued right through the seventeenth. It had been stimulated by the discovery of manuscripts and a revival of interest in ancient writings that had long been neglected. The Renaissance philosophers had initially been in reaction against the prevailing academic (Scholastic) philosophy. The Scholastics acknowledged Aristotle simply as “the Philosopher” but, while preserving some Aristotelian terminology, they developed a style of philosophizing that was found to be obscure and unfruitful. Partly in response to Humanist critics, Scholasticism was modified and enjoyed a new lease on life in the late sixteenth century. It continued to be the dominant form of philosophy in the universities of Europe for almost the whole of the seventeenth century.

Understanding the physical world was one of Leibniz's central interests. Earlier chapters of this Companion have explored aspects of Leibniz's metaphysics as they developed, his account of substance in general, and corporeal substance in particular. But Leibniz's interest in the physical world did not stop with metaphysics. Among his writings are numerous letters, notes, essays, and more extended treatments of questions in physics that show his deep engagement with the science of his day. Leibniz was one of the most important physicists of the late seventeenth century; other than Sir Isaac Newton, there is probably no other physicist of his generation who contributed more to the new mathematical physics. Thus, to understand the history of science in this crucial period, we must understand Leibniz's thoughts on physics. For Leibniz, as for many of his contemporaries, there was no clear boundary between philosophy and physics; understanding the world was at issue, and often those involved in what we would call philosophical projects to understand the world were also deeply involved in what we would consider scientific projects as well. Descartes, for example, the great philosopher of the earlier seventeenth century, made important contributions in his writings to mathematics and physics, as did Bacon, Hobbes, Gassendi, and later, Berkeley. Leibniz's physics and his philosophy were deeply intertwined; to try to study the one without the other is to get only a partial and inadequate picture of his thought.

Few philosophers today would go this far. Even in a period that has witnessed a dramatic rebirth of Anglo-American philosophical theology, the typical strategy has been to embrace a favorite proof while criticizing others or to maintain, more cautiously, that a particular argument has not been refuted. Nevertheless, while most of these philosophers reject the claim that all the classic arguments can be rendered sound, they also dismiss as passé the once prevalent view that proving God's existence is a hopeless task.

Natural theology, then, is on the rise. At such a time, it is reasonable to review the arguments of Gottfried Leibniz, one of its most distinguished proponents. Because he thought deeply about many of the issues that now absorb us, an examination of his ideas is likely to illuminate contemporary concerns.

Leibniz gives his own versions of four traditional proofs of God's existence: the ontological argument, the cosmological argument, the argument from eternal truths, and the argument from design. According to the ontological argument, God's existence follows a priori from his definition as an absolutely perfect being. Since existence is more perfect than nonexistence, the very idea of God entails that he exists. The cosmological argument, on the other hand, begins with the fact that something exists and derives the existence of God via a causal principle.

Leibniz claimed to be proud of the fact that, during his lifetime, he had no school, no disciples, and no popularizers. He despised, he said, the sectarian spirit which he associated with the Cartesians. Whether this attitude did not hide a kind of disappointment in the end is open to question. Leibniz was widely admired as a diplomat, a man of learning, and as a mathematician. But he was not, during his lifetime and long afterwards, considered a great philosopher, and after the deaths of Sophie Charlotte, the Queen of Prussia, in 1705, and her mother, the Ellectress Sophie, in 1714, no one showed an intense interest in his metaphysical theories. The dispute with Newton and the Royal Society, followed by the increasingly agitated argument with Newton's representative Samuel Clarke, threw a pall over Leibniz's last two years. Newton, never a gracious opponent, is said to have boasted that he killed Leibniz.

More than twenty years ago, Carl J. Friedrich offered this rather deflationary assessment of Leibniz's significance as a legal and political philosopher - that he was not “a thinker of the first rank on law and politics; no basically novel insight can be attributed to him.” Indeed, it must be admitted that Leibniz followed a traditional Christian reading of the divisions of natural law expounded in the Institutes of Justinian's Code (completed in 529 and revised in 534). It is also true that he resisted the trend toward independent sovereign states in favor of a return to a unified respublica christiana, to be achieved by revitalizing that practically defunct offspring of the medieval marriage of church and state, the Holy Roman Empire. But it must also be said that he developed a profound and inventive philosophical underpinning for the conventional legal wisdom.

Many people first came across the name “Leibniz ” when reading Voltaire's Candide, and the encounter is not likely to inspire confidence in Leibniz as a great philosopher. In Voltaire's biting satire, the optimism of Doctor Pangloss - whose character is based either on Leibniz himself or on his disciples - appears as a foolish and almost wickedly complacent response to the evils of our world. The reader cannot help but sympathize with Candide's rhetorical question: “If this is the best of all possible worlds, . . . what can the rest be like?” Even initial exposure to Leibniz's own texts is not always encouraging. Perhaps the most widely read of Leibniz's works is the Monadology, and although, in many respects, a brilliant summary of his final metaphysical views, it is not the best introduction to his philosophy. It is natural to feel, as Bertrand Russell once did, that we are presented with “a kind of metaphysical fairy tale, coherent perhaps, but wholly arbitrary”; ”art of the problem is that the fairy tale metaphysics is presented to us in a “take it or leave it”manner with little in the way of sustained argument. Initially, then, Leibniz's reputation as a philosophical genius of the first rank may strike us as puzzling.

Problems about the relations between Leibniz's philosophy and his logic have exercised scholars ever since Bertrand Russell's book on the philosophy of Leibniz, first published in 1900. The thesis of that book, as Russell expressed it later, was that “Leibniz's philosophy was almost entirely derived from his logic.” Russell's argument was that Leibniz derived from his logic his distinctive views about the nature of substance - that each substance is a genuine unity, a “monad”; that each created substance expresses the entire universe, and, strictly speaking, does not act on any other substance; that each substance is a soul, or at any rate soul-like; and that no substance resembles any other substance entirely. Russell also discussed Leibniz's views about contingency, about possible worlds, and about freedom. In this volume, Leibniz's views about logic and substance are discussed by Professor Sleigh in a separate chapter; I shall restrict myself to the topics of contingency, possible worlds, and freedom. This is not a haphazard group; there are close connections between Leibniz's discussions of these topics. Nor are the issues raised merely marginal; on the contrary, they take us to the very heart of Leibniz's philosophy.