As we have seen earlier, Descartes’ proffered solution to scepticism became embroiled in attacks, on the one hand from sceptics and on the other from dogmatic thinkers who did not share Descartes’ belief that he had found the new system of philosophy. Descartes’ followers tried to fend off attacks from the sceptics and the dogmatists while maintaining the basic elements of Descartes’ position. In the fifty years after Descartes’ death, the orthodox Cartesians attempted to fend off challenges from the Jesuits, from Spinoza, and from the new sceptics Simon Fouchet and Bishop Pierre-Daniel Huet. A good deal of this discussion is covered in Richard Watson’s two studies The Downfall of Cartesianism and The Breakdown of Cartesianism.1 In this chapter, I shall consider the way three of the major philosophers of the last quarter of the seventeenth century tried to avoid the pitfalls of Descartes’ system and to fend off sceptical attacks—Nicolas Malebranche, John Locke, and Gottfried Wilhelm Leibniz.
Nicolas Malebranche (1638–1715) was born in Paris, the son of a councilor to Louis XIV. He studied theology at the Sorbonne and, in 1660, entered the pious order of the Oratory, concentrating mainly on theology and Bible studies. The Oratory was founded by Cardinal Bérulle and was oriented toward Augustinian thought and training teachers and preachers. In the 1650s and 1660s the Oratory sought to avoid being labeled Jansenist because of its Augustinian orientation. Malebranche apparently first encountered Cartesianism in 1664 when he came across a copy of Descartes’ Traité de l’homme. He got very excited by this new system of philosophy. He was concerned about the problems exposed in the Cartesian “way of ideas” by which ideas were used to gain knowledge of external things. Problems had been raised about how ideas could lead us beyond the world of ideas and about how ideas could be used as means of studying something entirely different from an idea. Malebranche worked out a revised Cartesianism, which he presented in his Recherche de la Verité.2
The first volume of Recherche appeared in 1674 and the second volume in 1675. Malebranche showed practically no interest in the writings of sceptics, ancient and modern. He had a short chapter on Montaigne, just dismissing him as a pedant, and Sextus is mentioned only once in a footnote.3 The central interest was in a key problem in Descartes’ philosophy, which opponents had pounced on to generate sceptical puzzles. For Descartes, genuinely certain knowledge consisted of clear and distinct innate ideas that God had given us and from which we inferred the nature of a reality outside of us. Thus, each human being possessed his or her own set of innate ideas and used them individually to ascertain what was true about the world. Malebranche was aware of how the connection between Descartes’ innate ideas and the world had been bitterly criticized by thinkers like Gassendi and how this criticism created a scepticism about any knowledge of external reality. To obviate this, instead of following Descartes’ journey from the ideas in our minds to knowledge of reality, Malebranche insisted that what we know is in the mind of God, not in ourselves, and genuine knowledge is about what he called “intelligible extension.”4 This is not to be confused with the sensory ideas we have of extended things. These perceptions, he declared, were feelings rather than intelligible knowledge. The guarantee of our knowledge is that it is in the divine mind; in his most famous phrase, “we see all things in God.”5
Further, Malebranche pointed out that all that we know and can know is about intelligible extension. This gives us mathematical certainty and the basis for physics. It does not tell us, however, whether there is a physical world above and beyond our ideas. Malebranche said that the only evidence we have that there is a physical world is that the Book of Genesis tells us that God created heaven and earth. If we believe Scripture, then it is by revelation, not by observation or reasoning, that we come to know of a physical world.6
Malebranche pushed another aspect of Descartes’ theory probably further than Descartes would have. For Malebranche, all causation comes from God. Descartes had claimed that God continuously creates the world. Malebranche has God continuously causing every event in the world. In his analysis of the causal sequence of events, Malebranche said that there is nothing in a prior event that necessarily causes a subsequent event. There is no necessary connection or logical connection. The only cause is God, and, fortunately for us, God acts according to general laws of his own willing, so that we find constant conjunctions of divinely willed events and can expect this type of pattern to continue indefinitely. In an example that he made famous, if one billiard ball moves toward another, there is nothing in the motion of the first ball that implies or ordains that it will move another one. When they strike, it is on this occasion that God wills the motion of the second ball.7 Malebranche’s view is called occasionalism, in which God alone is the causal agent and all actions are occasions of God’s will.
Malebranche thought his system would be impervious to sceptical criticism since he had removed the areas of Cartesian thought that had proven so fraught with difficulties. Transforming the process of gaining knowledge from our minds to some source of truth, Malebranche had made our knowledge a kind of Augustinian illumination. God makes it possible for us to know and provides the knowledge and therewith the guarantee of it. The bridge between our knowledge and knowledge of reality is no longer needed since we only know all things in God, not in ourselves. Then the mathematical Cartesian system can be applied to intelligible extension and yield a necessary system of physics, which perhaps corresponds to a real physical world, if God has created one. We can work out the mathematical laws of physics; in addition, we can learn about the sequences of perceived events as occasions of God’s willing certain types of occurrences.
If Malebranche thought that his Augustinian mathematical system would be free from sceptical questioning, he was quickly disillusioned. Almost immediately after the first volume of the Recherche appeared, a sceptic, Simon Foucher, whom I will consider in the next chapter, lodged a series of sceptical attacks in which he tried to show that some of the same problems that plague the Cartesian system apply just as well to Malebranche’s. A later opponent, the Jansenist Antoine Arnauld, carried on a twenty-year-long controversy with Malebranche in which Arnauld kept trying to show that Malebranche’s system led to the most dangerous and absurd Pyrrhonism. Others attacked Malebranche as having introduced a new form of Spinozism, since Malebranche’s world would only consist of God and the illuminations coming from him.8 And some of the opponents, including Arnauld, insisted that Malebranche would end up having God the author of all human events and hence of evil ones as well as good ones. God would have to be the cause of a bullet emerging from a gun and then be the cause of the bullet entering another human being and then be the cause of the heart of the other human being ceasing to function.
Malebranche furiously insisted that there were ways that human culpability and responsibility could still be meaningful in his system. He also kept insisting that he had avoided the worst pitfalls in the Cartesian system and made knowing a religious activity that was thoroughly authenticated by the author of it, the Divine Being.
Some saw that Malebranche’s unexciting explanation of how we find out about the existence of a material world is rather far-fetched. People do not consult the Bible to find out whether trees and mountains and rivers exist outside of them. The status of the statement in Genesis that God created heaven and earth does not seem to play any serious part in undergirding knowledge of the external world.
Perhaps the most critical sceptical challenge against Malebranche was that of Pierre Bayle. The great sceptic was perhaps the first to try to present Malebranche as a major figure in the contemporary philosophy of the time. He personally got involved with Malebranche in editing and publishing a volume of essays by various post-Cartesian philosophers, including Malebranche. He described him in various writings as one of the most important philosophers of the day. However, he then went on to insist that when one had seen the beauty of the system Malebranche had developed one also had to realize that the system, like that of Leibniz, while thoroughly consistent, was not believable by ordinary mortals. It flew in the face of ordinary common sense and general human beliefs. The more one presented the ingenuity and consistency of the system, the less credible it became.
As an example of making the Malebranchian system incredible, John Locke wrote a work called An Examination of P. Malebranche’s opinion of seeing all things in God.9 Locke, with his empirical outlook, tried to take Malebranche’s claims at face value while ignoring the metaphysical dimension involved. So Locke insisted it was nonsense to say that we see all things in God. We see things, in fact, in time and space around us. Locke deliberately or otherwise managed to miss Malebranche’s point but brought out how counter it was to people’s normal experience and beliefs.
John Locke (1632–1704) became involved in sceptical problems not only from his English training and associations but also from foreign influences when he was for several years in France and, later on, for several years in the Netherlands. In France he was in association with some of Gassendi’s disciples. He also seems to have met Bishop Huet at least once at a scientific gathering in Paris. Later on, when he was a refugee in the Netherlands, he came to know Pierre Bayle and some of his leading opponents, including Philip van Limborch and Jean Le Clerc. The latter was often involved in fighting off various forms of scepticism that were appearing in print at the time. Locke stayed in touch with Limborch and Le Clerc and discussed various philosophical issues of the day with them. Locke also reviewed some of the current intellectual literature for Le Clerc’s journals Bibliothèque Universelle and Bibliothèque Ancien et Moderne. When Locke returned to England in 1689 his secretary, Pierre Coste, was a close friend of Pierre Bayle. In Bayle’s correspondence with Coste he usually sends his warmest regards to Locke. Coste later translated Locke’s Essay into French, and it was Coste’s translation that was read by most of the French Enlightenment figures. So Locke, when he came to publish his philosophy (in some cases long after it was written), should have been well aware of the sceptical issues involved in the positions he took.
Locke no doubt knew, or had heard of, both Bishop Wilkins and Joseph Glanvill, in view of their involvement in the 1650s at Oxford with Robert Boyle and the early scientific work there and then later with the Royal Society. Locke was at Oxford at the time that Wilkins was creating the Invisible College, but we have no information that Locke took part in their experiments. However, he was taught by some members of the group and, in later years, was close to Boyle and other leading figures in British scientific affairs of the time. One of Locke’s earliest writings is a preface to Thomas Sydenham’s treatise on fever. There Locke set forth the mitigated scepticism of the Royal Society outlining what could and could not be known about medical problems. He came to know Isaac Newton. At the time Newton had completed Principia Mathematica, Locke and Newton had many discussions of scientific and religious matters.10 Locke had been working on his study of the origin, extent, and certainty of our knowledge over many years. The final version was completed in 1689 and published in 1690. Starting from the empirical perspective that all our knowledge comes to us via the senses, Locke quickly developed a scepticism about the possibility of human beings possessing any innate knowledge, such as had been claimed by Herbert of Cherbury and Descartes. A more sceptical side of this view appeared in his discussion of our knowledge of any external substantial reality. We perceive clusters of qualities and give them names like table, chairs, stones, grass; however, if we are asked to specify what holds together these clusters of qualities or what lies under the sensations, Locke said, “it is something I know not what.” Since we do not have experience of any power that holds the clusters of qualities together, and we do not know the real essence of any of these clusters, we are left in a scepticism about what it is that forms the substratum of our experiences. Locke insisted that although we do not know what it is, we find that we have to believe that there is something that constitutes the foundation of our experience. In his famous example, he told of the Indian philosopher who was asked what the world was founded upon and said that it was sitting on the back of an elephant and when asked what the elephant was standing on he said the back of a turtle and when asked further, he replied: “I know not what.” The discussion of the problem of knowing the actual substances that make up the world leads to a sceptical limitation of what human beings can know. Not only are we unable to know the underlying substratum, but we can only know its characteristics from our experience. It can possibly have many other characteristics, and so Locke in another notorious passage said that we can never know enough about matter to tell whether it is capable of thinking and enough about mind to tell whether it might be extended. These two substances, body and mind, which were so central to Descartes’ philosophy, become blurred in Locke’s account. This even led to Locke being accused of Spinozism since thinking matter and extending mentality could both be the same underlying substance that appears in Spinoza’s metaphysics.
Locke tackled the problem of the certitude of our knowledge in the fourth book of the Essay, where he developed an account somewhat like that of Glanvill and Wilkins. Locke was not concerned to argue about the reliability of our faculties. He took for granted that our God-given faculties are what provide us access to knowledge. The question is: What can we actually know, and how certain can such knowledge be? Locke apparently did not take the Cartesian possibility seriously but only considered that we might misuse or misapply our rational faculty. Therefore, we have to be careful, and make sure that we were not committing any mistakes, and have our mental attention fixed on clear ideas. Locke did not consider the possibility that we might be mistaken in thinking we have avoided the possibility of mistakes.
The closest Locke seemed to get to considering radical Cartesian scepticism was when he briefly discussed Descartes’ dream hypothesis. If “any one will be so sceptical, as to distrust his Senses, and to affirm, that all we see and hear, feel and taste, think and do, during our whole Being, is but the series and deluding appearances of a long Dream, whereof there is no reality,” and is thus led to question the existence of all things, “or our Knowledge of any thing,” Locke then deflected this sceptical possibility by pointing out that the raising of it could be part of a dream too. Although this does not directly deal with the sceptical problem, it was sufficient for Locke to make it look like the Cartesian hypothesis was silly and not worthy of an answer. “If all be a Dream, then he doth but dream, that he makes the Question; and so it is not much matter, that a waking Man should answer him.”11
Immediately after dismissing the sceptic, Locke indicated that his own theory of knowledge only led to a most limited account of what we could know and how reliable such knowledge is. Our knowledge “is not only as great as our frame can attain to, but as our Conditions needs. For our Faculties being suited not to the full extent of Being, nor to a perfect, clear, comprehensive Knowledge of things free from all doubt and scruple; but to the preservation of us.”12
For Locke, there are three types of knowledge; intuitive, demonstrative, and sensitive. The most certain knowledge, according to Locke, is intuitive knowledge. This type of knowledge “is the clearest and most certain, that humane Fraility is capable of.” It is irresistible, and “leaves no room for Hesitation, Doubt, or Examination.” All human certainty and evidence of any knowledge depends on this kind of intuition, and one cannot ask for any greater certainty. “He that demands a greater Certainty than this, demands he knows not what, and shews only that he has a Mind to be a Sceptick, without being able to be So.”13 Intuitive knowledge is what we are immediately aware of when we have an idea or when we compare two ideas. It is intuitively certain that white is white and that white is not black. Our intuitive knowledge extends only to ideas that we can clearly compare with themselves or with each other.
For Locke there is no possibility of asking whether this intuitive certainty can be deceptive, or can be the result of some deceptive distortion of our faculties. It is the greatest assurance we have or can ask for. What can be inquired into is when and under what conditions we do in fact have the sort of unquestionable assurance. Locke is perfectly willing to admit that in particular cases where we think we possess intuitive knowledge, we can be mistaken. We may confuse names or words with ideas. Or we may think an idea to be clear when it is not so. In such cases our intuitive perception may be faulty. But this does not mean that our knowing faculty can be deceived.
The second kind of knowledge is demonstrable knowledge, which is the comparison and agreement of two ideas in terms of an intervening idea. Each comparison is an intuition. The string of intuitions becomes a demonstration if each step can be clear in our memory. So, for Locke, the shorter the number of steps involved in the demonstration, the greater the certainty. Locke contended that one could have demonstrable knowledge not only with mathematical concepts but also concerning the existence of God and the principles of ethics.
Sensitive knowledge is our sole means of knowing what exists outside of us. We have it when we are aware of something beyond our own internal experience. Our knowledge of the world is mostly this kind of sensitive knowledge. Locke defends it as being a real part of our mental world by pointing to the involuntary character of our experience. Compared with the ideas that we can manipulate at will and with the resistance of items and experience to our volitions if somebody raised sceptical problems about whether what we experience is really in the world, Locke just dismisses this and suggests that the sceptic try putting his hand in the fire or walk into a wall and said sceptic will no longer be so dubious.
These three kinds of knowledge tell us fairly little about the real existence of things. Locke claims that intuitively we can only know the real existence of ourselves, demonstratively we can only know the real existence of God, and by sensitive knowledge we can only know the real existence of something at the time that we have the experience. An underlying scepticism comes in when we try to explain why we have the involuntary experiences we do and what could possibly be the causal features that impinge on us and that might account for the constancy and coherence of experience. Locke realizes some of the sceptical results of his inquiry when he declares that there can be no real science in the sense of necessary knowledge about what is going on in the world. Limited certainty is possible in much the same way as Wilkins and Glanvill had contended, and in most matters probable knowledge rather than certain knowledge is all that we can obtain but is also all that is needed for human activities.
Locke then developed a sort of semiscepticism that could be read as a justification for empirical science. His position could also be read as a type of realist philosophy, providing enough bases for external knowledge without contending that we could know anything beyond experience. As we all know from introductory philosophy courses, Locke’s compromises were then dashed by Berkeley and Hume, and, as Berkeley said, he was left with a forlorn scepticism in his attempt to defend the external reality of any of our experiences.
In fact, Locke was almost immediately attacked as being a purveyor of scepticism and a denier of the doctrine of the Trinity because there could be no certain knowledge of it. Bishop Edward Stillingfleet got into a bitter controversy with Locke regarding the sceptical possibilities of Locke’s system. Bayle is the only one of the French sceptics who took note of Locke, and he just spoke of a few minor points. In the early eighteenth century, when Coste’s translation appeared, Locke was almost immediately taken over by French thinkers as a sort of semisceptic. This was due not only to Locke’s wavering middle ground between scepticism and dogmatism but also because Coste’s translation emphasized the sceptical features and so steered his audience to seeing Locke more as a sceptic than a realist.
In sum, for Locke we can have as complete a certainty as possible about our ideas and the comparisons between them. Knowledge beyond this is extremely limited because our faculties, rational and sensory, are not adequate to provide us much access to knowledge of real existing beings (other than ourselves and God) but are adequate to provide us enough quasi-knowledge suited for our preservation and ability to function.14 The radical scepticism about the very nature of our faculties and about whether they can be deceptive does not come up. Only the application of the faculties can be deceptive.15
Gottfried Wilhelm von Leibniz (1646–1716) was more involved with sceptics and scepticism than any other philosopher at the end of the seventeenth century. He was personally involved with the three leading sceptics of the time, the abbé Simon Foucher, Bishop Pierre-Daniel Huet, and Pierre Bayle. Several of his most famous presentations of his philosophy were published as answers to these sceptics or to deal with problems they had presented to him. Perhaps the best-known statements of Leibniz’s metaphysical views are the letter to Foucher; the “Nouveau systeme” of 1695, in which Leibniz first published his theory of the preestablished harmony; his letter of 1697 to Nicaise on Cartesianism, inspired by Huet; his answer to Bayle’s article “Rorarius” of 1698; and the Theodicée of 1710, a fulllength discussion of some of Bayle’s sceptical theories. In fact, Leibniz considered his letter to Foucher in the Journal des Sçavans, and Bayle’s discussion of it in the article “Rorarius” the best presentations in print of his new metaphysical theory.
While Leibniz was certainly no sceptic, nor a man who was particularly concerned with la crise pyrrhonienne of the seventeenth century, he was regarded as a closer friend intellectually by the sceptics of his age than any of the other metaphysicians of the period. While Foucher, Huet, and Bayle continued a steady and devastating attack against Cartesianism and against the views of Malebranche, Arnauld, Spinoza, Cudworth, and Locke, they treated the possibly more fantastic metaphysics of Leibniz with a degree of respect and restraint that had probably not occurred in any previous controversies between the sceptics and the dogmatic philosophers. At the same time that metaphysicians like Arnauld, Malebranche, and Berkeley regarded it as their mission to destroy the sceptical menace, “the spectre haunting European philosophy,” Leibniz is exceedingly calm and unanxious in his treatment of the challenges to rational thought raised by his friends. At a time when so many others could only see the sceptical arguments as so dangerous they would overthrow all certainty in natural and revealed knowledge, and could only see the sceptics as demonic figures bent on destroying all trust in the Christian worldview, Leibniz found great value and inspiration in the doubts of his friends. At the same time that various German philosophers and theologians were debating whether Solomon or Job was the founder of scepticism (and concluding that it was really the devil),16 Leibniz could conclude that his best and most valuable critics were the sceptics, whose doubts, instead of issuing in the destruction of the rational and religious world, could lead to the discovery of the most beautiful basic principles of philosophy and theology. Finally, while the sceptics were attacked on all sides as fiends, unworthy of the positions they held, and while French Calvinists persecuted Bayle in Holland, and fanatics like Arnauld tried to expose the pernicious menace of Huet, Leibniz treated them as his dearest friends for whom he would do anything. When the magistrate of Rotterdam condemned Bayle and removed him from his post, Leibniz sought to find him a new job in Germany.17
Leibniz was introduced to sceptical problems at least as early as his college days at Altdorf. One of his professors had written and published an answer to Francisco Sanches and had published Sanches’ sceptical attack on mathematics, his letter to the mathematician Clavius. Leibniz seems to have taken some of the sceptical points seriously and continued discussing them with mathematicians throughout his life.
He really became immersed in sceptical discussions when he went to Paris on a diplomatic mission starting in 1672. In Paris he met Foucher and Huet and, later on, came into contact with Pierre Bayle.
After returning to Germany, Leibniz was interested in discussing the problems Foucher raised, growing out of the latter’s polemic with Malebranche. Foucher sent Leibniz all his works, and often Leibniz gave them most careful and detailed examination, showing them far more respect than almost any other contemporary. Not until Foucher’s death, and Leibniz’s interchanges with Bayle, did Foucher receive a lowering of status in Leibniz’s eyes. In 1684–85, when Leibniz developed his theory of the preestablished harmony, he sent it to Foucher for his criticisms. And in the 1690s, as Leibniz formulated his theory more clearly, his letters to Foucher, and Foucher’s answers, were used as the first public presentation of the new metaphysics (published, mainly through Foucher’s efforts, in the Journal des Sçavans). In 1692 and 1693, some of Leibniz’s views (and Foucher’s comments) appeared in this journal, and finally in 1695, the letter to Foucher, “Systeme nouveau de la nature et de la communication des substances, aussi bien que de l’union, qu’il y a entre l’ame et le corps” appeared, expounding Leibniz’s full theory for the first time. Shortly afterward, Foucher’s answer was printed, followed by Leibniz’s éclaircissements in 1696. Leibniz waited anxiously for Foucher’s answer but learned to his sorrow that his sceptical friend had passed away.18
The Huet-Leibniz relationship does not seem to have generated any controversy. Each had the greatest respect for the other, and each was delighted to learn that the other approved of his latest efforts. Leibniz seems to have regarded Huet as a person of immense erudition, a supreme authority on questions about the classical world and the history of religion. He also speaks very highly of Huet’s critique of Cartesianism and offers new evidence to be used in the next edition of Huet’s Censura. Leibniz prepared some of his own animadversions to Cartesianism as a possible supplement to Huet’s work, and finally in the 1690s published some of his attacks on Descartes’ philosophy at the suggestion and insistence of Huet.19 After Huet retired into oblivion and senility, although neglected by almost everyone else, he was still remembered by Leibniz, who always asked his friends going to Paris to deliver a message to the bishop.
But it was with Bayle that Leibniz had perhaps his liveliest and most important exchanges of ideas. It is doubtful if Leibniz ever met Bayle personally. Their first identifiable contact seems to be from 1687, when he sent Bayle a letter about an article of the abbé Catelan that had appeared in Bayle’s Nouvelles de la Republique des Lettres. Leibniz says in his letter: “What pleased me most in the reply from M. l’Abbe C. that you inserted into your instructive Nouvelles from last September, was that it gave me the occasion to make the acquaintance with a person of your merit.”20 Bayle printed a letter of Leibniz in the Nouvelles shortly thereafter. A couple of years later, we learn from a letter of Leibniz to Bayle’s friend Henri Basnage de Beauval that Leibniz was very anxious to obtain Bayle’s views on his animadversions on Cartesianism.21 But Bayle only remarked that Leibniz’s piece “m’a paru belle,” was worthy of a strong and mathematical mind, and that he, Bayle, still remained unconvinced.22 Leibniz tried hard to elicit some detailed criticisms, not, as he insisted, in order to start a dispute, but in order to make his anti-Cartesian views better.23 But Bayle was working feverishly compiling the great Dictionnaire and warding off the attacks pressed by his erstwhile colleague Pierre Jurieu. Leibniz’s letters to Basnage de Beauval show a continuous sympathy for Bayle in his troubles with the Calvinists of both the orthodox and liberal factions. Leibniz was so concerned that in 1697 he tried to get Bayle a post as librarian in Kassel where he would be left in peace.24
The publication of Bayle’s Dictionnaire began a new stage of the relationship of Leibniz and Bayle. After years of trying to get philosophers like Malebranche and Locke to consider his new system, Leibniz found that Bayle considered him one of the foremost metaphysicians of the age and devoted a long note to a statement and criticism of the theory that Leibniz had propounded in his published letter to Foucher of 1695. For the first time, Leibniz saw himself discussed as an important philosopher with a theory rivalling that of Malebranche. In the article “Pellisson,” Bayle complimented Leibniz for his ability to write so well in French, and then said, “He is one of those rare men who do not find themselves limited to the sphere of human merit.”25 In the article “Rorarius,” Bayle said in discussing some difficulties about the vexing question whether beasts have souls, “There are some things in Leibniz’s hypothesis that cause difficulties, though they indicate the extent and power of his genius.”26 This was followed by a statement and criticism of Leibniz’s theory. Bayle declared that he was not yet willing to prefer Leibniz’s theory to that of Malebranche, and he was waiting until “its able author has perfected it.”27 Leibniz set to work immediately and published a letter in Basnage de Beauval’s journal, Histoire des Ouvrages des Sçavans, answering Bayle’s points, and then anxiously awaited developments.28 But, more important, a note was added of several folio pages discussing Leibniz’s answer. Bayle was delighted that his objections had led Leibniz to develop his views, and, Bayle said, “I now consider this new theory as an important conquest that enlarges the bounds of philosophy.”29 Bayle’s objections showed that he was still not convinced, but he considered Leibniz’s theory as one of three possible ones, of equal importance to that of the Cartesians and the Scholastics. Leibniz immediately published a reply in the journal Histoire critique de la republique des lettres of 1702.30 Bayle refused to go on debating the matter, and told Leibniz that all he could do was keep repeating his same objections, and that he remained unconvinced.31 Both Bayle and Leibniz seem to have been most pleased with their exchange, although Leibniz appeared to regret that it ended so soon. In an overoptimistic mood, Leibniz wrote Thomas Burnett in 1706 that the reason Bayle had given up discussing Leibniz’s theory was that he would have been obliged to give up his scepticism.32
Leibniz was concerned with other views of Bayle and frequently discussed them in his letters. Bayle’s “fideism” and his attack on the compatibility of reason and faith intrigued Leibniz. He reports that he discussed Bayle’s objections with the queen of Prussia at great length. Basnage de Beauval tried to interest Leibniz in entering the arena with Bayle on this score, but Leibniz was not willing. He seemed to be concerned that those like Jurieu, Le Clerc, Jaquelot, and others, who were busily arguing with Bayle in print, were only encouraging Bayle to be more extreme in his statements. After Bayle’s death, Leibniz put together his answers to Bayle’s views on faith and reason, and on the problem of evil, and published them as the Théodicée.33
One of the most surprising aspects of the discussions and debates between Leibniz and the sceptics is the aura of sweetness that pervades them all. Unlike the various acrimonious debates in seventeenth-century philosophy, such as those between Descartes and Gassendi, or Malebranche and Arnauld, Leibniz and his sceptical friends go out of their way to be kind and flattering to each other. And in their correspondence, both to each other and to others, they never criticize each other’s character or ability. In fact, at a time when everyone was denouncing sceptics, and the sceptics were most forcefully denouncing dogmatists, one finds a tranquil interchange of ideas taking place between one of the major dogmatists and the three sceptics of the period. And at a time when Bayle was being denounced right and left as the menace to reason and religion, and Bayle was castigating his opponents as forcefully as they attacked him, Bayle and Leibniz could discuss each other’s views with a surprising and almost unnatural calm, and could defend each other’s character. In fact, when one turns from the controversial world of the late seventeenth-century to the little world of Leibniz and his sceptical friends, it is hard to believe that such peace and quiet, and such admiration and goodwill, could exist between any opponents in that day and age.
Why did Leibniz and the sceptics get along so well, and why should they have been interested in each other’s views, and have admired each other’s ideas so much? Leibniz’s metaphysical theory does not appear to constitute a contribution to sceptical argumentation, nor do the renovated sceptical puzzles of Foucher, Huet, and Bayle seem to aid or abet a metaphysician in his quest for the nature of reality. The mystery of the idyllic relationship between Leibniz and the sceptics can be solved by examining some of the content of their discussions, and some of their comments about their discussions.
On the one hand, Leibniz, although certainly not a philosophical sceptic, agrees with some of the major contentions of the sceptics, and is willing to admit, unlike other metaphysicians of the seventeenth century, that there are general, and perhaps unanswerable, objections that can be raised against any philosophical theory. In his discussions, especially with Foucher and Bayle, Leibniz agreed that there are first principles of philosophical reasoning that have not been satisfactorily demonstrated. In a letter to Foucher of 1692, part of which appeared in the Journal des Sçavans,34 Leibniz said that he thought the sceptics were quite reasonable in stressing this point and that they were rendering a service in pressing people to discover demonstrations of the first principles they employed.
In addition, one finds that in most of his discussions with the sceptics, Leibniz was willing to regard metaphysics as a hypothetical enterprise, that is, as an attempt to present theories that agree with the known facts, that avoid certain difficulties in previous theories, and that give a satisfactory or adequate explanation of the world that is experienced. In the published discussion with Foucher of 1695–96, and the debate with Bayle over the article “Rorarius,” Leibniz does not argue for his theory as the true picture of reality, but rather as the most consistent hypothesis to explain the known scientific facts, and the general conclusions of the “new philosophers” about the relation of the mind and the body, and to avoid the “unfortunate” complications or conclusions of the views of Descartes, Malebranche, or Spinoza. In the first answer to Bayle, Leibniz spoke of his theory of the preestablished harmony as “a possible hypothesis, and suitable to explain phenomena.”35 When Foucher and Bayle insisted that one could not tell if Leibniz’s theory was true, or even if it were possible that the universe was so constructed, Leibniz answered that although it was desirable to demonstrate the truth of his principles, all that he was insisting on was that they were consistent with the known evidence and involved less unreasonable claims than Descartes’ or Malebranche’s. And when Bayle pressed the commonsensical objection that one could not reconcile Leibniz’s theory with popular notions about the universe, Leibniz brushed this aside, saying that he was only concerned to claim that his theory did not contradict any accepted principle of reasoning and that it was compatible with all the facts, that is, that it was a good hypothesis. And as long as Leibniz and the sceptics could treat the new system as a hypothesis, they could debate the detail of Leibniz’s theory without floundering on the traditional sceptical difficulties, which Leibniz was usually willing to recognize—that the foundations of the theory could not be demonstrated.
Further, Leibniz agreed with the sceptics, against the metaphysicians of the seventeenth century, that our knowledge of the external world is not of external reality but only of the relations of phenomena. Foucher labored all his life to prove that the Cartesian system provided no knowledge of the existence or nature of the real world outside of us. By and large, Leibniz agreed, saying that we could only discover the system of relationships of the phenomenal world. According to Leibniz, the sceptics throve on a mistake of the dogmatic philosophers, that of seeking to attribute phenomenal experience to a physical substance.36
The last major philosophical view in which Leibniz was in partial or complete agreement with the sceptics was their anti-Cartesianism. For the sceptics, Cartesianism represented the dogmatism that had to be destroyed, and so they had to modernize their arguments to meet the new foe. For Leibniz, Cartesianism was an inadequate theory to explain the new scientific world. The sceptics and Leibniz could agree on the major failings of Cartesianism, although they were hardly in agreement as to what to do about them. They were all agreed in opposing the pompous, dogmatic, sectarian pronouncements of the Cartesians claiming a unique way to truth. Leibniz and the sceptics were all humanists, and found great value in the tradition of man’s effort to understand his universe; hence they rejected the Cartesian attitude toward the past. They also agreed that the fundamental Cartesian rule of truth, the doctrine of clear and distinct ideas, was inadequate to discover the truth, and they agreed that the essence of matter was not extension. And they delighted in telling each other new arguments and new stories to oppose and ridicule the Cartesian philosophy and its status in the intellectual world. Leibniz, in his desire to present his own theory, was glad to join with those who were criticizing his predecessor.37
In sum, Leibniz and the sceptics could get along philosophically within a certain area of agreement, since Leibniz agreed to some extent with the sceptical claims as to how little demonstratively established knowledge we could have, how restricted was our knowledge of the world of experience, and how unjustified were the dogmatic claims to certain and necessarily true knowledge of the Cartesians. The basic and irreconcilable disagreement between Leibniz and his sceptical friends arises over how to deal with these difficulties. Leibniz was unwilling to see these limitations on our knowledge as a reason for sceptical despair, or to see these points as constituting a radical scepticism that cast whatever knowledge we had in any serious doubt. For Leibniz, whatever merits the sceptical arguments had, they did not have to lead to negative or destructive conclusions. At best, scepticism should be a spur to constructive theorizing, and not a reason for doubting or despairing of the possibility of knowledge.
Basically, the disagreement between Leibniz and the sceptics starts from the fact that for Leibniz it does not follow that because first principles have not, or even cannot, be proven, they are therefore uncertain. He pointed out to Foucher that the doubts of the Academicians and of Sextus Empiricus are good to start with, but these doubts should be used to search for first principles and not to despair of this search.38 And the mere fact that the principles cannot be proved should not prevent one from using the principles. One has to begin somewhere, and so, Leibniz suggests, one should begin as the geometers do, assuming the fewest principles (thus leaving the minimum number still to be proven), and then advancing logically from there. These “verités hypothetiques” can then lead us, if we proceed carefully, to settling many disputes and discovering many “belles principes.”39
The harrowing doubts of a “scepticism with regard to reason” do not affect Leibniz at all. He is unimpressed and unworried by the possibility that these assumed principles might be false or uncertain, or that we might err in reasoning from them. Neither Descartes’ demon hypothesis nor Bayle’s campaign for a rejection of the most evident and certain maxims of reason affected Leibniz. The fundamental principles of logic and of mathematics cannot be doubted or considered as false without making rational discourse impossible. As he told Foucher, concerning the principles of logic, “You even grant them in writing and in reasoning, otherwise you could defend at each moment everything contrary to that which you say.”40 Bayle’s claim that reason is unable to answer the false arguments against religion Leibniz rejects, saying, “it is to overturn everything in the light of reason, and admit something false could be demonstrated.”41
For Leibniz it makes no sense to question the bases of reason, since if these were doubtful, we could not be rational. And throughout, Leibniz has an unquestioning faith that we live in a rational world, and that we can and do think rationally. He made this clear in his comments on Sextus Empiricus from 1711, when he refused to get forced into defending rationality. The Cartesian supposition that this rational world might be a false or illusory one is rejected as an unintelligible hypothesis.42 But not only are the principles of reasoning unquestionable for Leibniz—so is the application of our reasoning faculty. The sceptical problems about whether we can be certain of our employment of the methods of reasoning are dismissed by insisting that to reason correctly one only has to calculate, and it is intuitively obvious, if one is careful, when one has performed the calculation correctly.43
In Leibniz’s refusal to entertain a scepticism with regard to reason, he shows that he never really took the destructive side of scepticism seriously. Leibniz’s rational faith precludes consideration of the radical side of the sceptical attack. The problems that shook the seventeenth century, the quest for certainty as a resolution of la crise pyrrhonienne, did not bother the ever-rational Leibniz. The harrowing possibility of the nouveaux Pyrrhoniens and of Descartes’ demonism, that we live in a fundamentally irrational and unintelligible world, was sloughed off by Leibniz as meaningless, or as a denial of the principles of reason. And, perhaps, just because Leibniz did not take the extreme side of the sceptics’ attack seriously, he could be extremely amiable about his arguments with them. Other philosophers saw the sceptics as the greatest of menaces to mankind because they cast all in doubt and hence could not treat them calmly, or regard them as friends. The sceptics had to be overthrown, or man was forever lost in a sink of uncertainty and error. The anguish of Pascal, seeking certainty through God, the dramatic overturning of scepticism by doubt by Descartes, left Leibniz cold, since there was no problem for a rational man. Leibniz was, perhaps, unique in his age as a man not engaged in the sceptical crisis and hence not required to do anything to resolve it. Since he had not the doubts of the sceptics nor the assurance of the dogmatists he could enjoy the battle of wits with his sceptical friends, without being fearful over the stakes at issue, and he could enjoy trying out possible ways of avoiding the sceptics’ conclusions.
Since ultimately Leibniz did not take the sceptics’ position seriously, it seems odd that he pursued his discussions with them all his life, and that he studied so many sceptical texts.44 To an extent, Leibniz was both enough on the sceptics’ side so that they could not argue and so far removed that they could not argue. Ultimately it seems their dialogue was more for psychological than for philosophical reasons. Leibniz offers two main explanations for why he liked to dispute with the sceptics; first, that one could argue with them without getting into a personal vendetta, and second, that he derived great stimulation from trying to answer their ingenious objections. It is probably for the latter reason that he placed Bayle and Foucher at the top of his list of opponents.
In the current of seventeenth-century controversies, Leibniz apparently disliked the level of abuse and ad hominem argumentation and mud-slinging. He seemed quite hurt when a German professor, Sturm, questioned his intelligence and sanity, and he greatly disapproved of the invectives in the polemics of Arnauld versus Malebranche, Bayle versus everyone, and so on. With Foucher, Bayle, and Leibniz there was sufficient mutual respect that they could challenge each other’s views without attacking each other’s character.45 Leibniz wrote to Jaquelot, one of Bayle’s exasperated opponents, that he enjoyed even specious objections, because, by answering them, one finds clarification.46
After Leibniz’s death, Pierre Desmaizeaux, in the preface to his collection of writings of Leibniz, advanced the possibility that Leibniz just enjoyed the dialectical game and did not care where it led. Desmaizeaux cited a letter from the German theologian Pfaff. Leibniz had asked Pfaff what he thought of the Théodicée as an answer to Bayle. Pfaff replied that he thought it really made Bayle’s views plausible, and that he surmised that Leibniz was not really serious in advocating his own system but was only diverting himself. Leibniz responded on May 11, 1716 (the letter was published by Pfaff in the Acta Eruditorum of 1728), that of course Pfaff was right, and he, Leibniz, was surprised that no one else up to now had guessed that he was only diverting himself. And, Leibniz insisted, a philosopher is not always obliged to be serious in making hypotheses. There is some question as to whether this letter is genuine. It does not appear in any of the known collections of Leibniz materials. Ezequiel de Olaso spent many years looking for it and was unable to find any trace. On the other hand, there is nothing that we know about Professor Pfaff to suggest he would fabricate letters of his late friend.47 The letter Pfaff quotes may have been a jest and may have no bearing on what Leibniz actually believed.48
We do know, thanks to Olaso’s researches, that Leibniz started a commentary on Sextus Empiricus around 1711. Leibniz indicated to others that he was going to go over the entire Pyrrhonnian text and show its weaknesses. In the 1718 edition of Sextus Empiricus, Leibniz’s refutation is listed as a work to be expected. However, Leibniz died before getting very far into this. Leibniz had explained to a learned Italian visitor that there were a few books that were central to his philosophizing and showed him his special collection, which included, of course, Plato and Aristotle and Sextus Empiricus, among others.49
The few pages of his commentary that do exist show his remarkable way of dealing with the basic sceptical questions. Olaso has very carefully shown Leibniz’s interest in sceptical problems from his earliest writings through the Théodicée.50 If we look at the fragment Leibniz wrote about Sextus, we can gain understanding of his appreciation and refutation of scepticism.
Olaso found that Leibniz had written a small analysis of some of the main arguments in Sextus in book 1 of the Pyrrhonian Hypotyposes, saying that all the important views are therein contained. The writing is unfinished. What has survived is about twenty-five hundred words on twelve pages. The fragment is not dated but seems to be referred to by Leibniz in four letters of 1711–12 and 1716.51 A possible reason for Leibniz’s working on the subject was that he had told J. A. Fabricius that he was preparing a refutation of Sextus. Fabricius quotes Leibniz as saying that Sextus was a subtle and learned writer,52 who is little known but nonetheless very helpful to the understanding of the philosophy of the ancient Greeks.53
Leibniz separates the dogmatists from the Academicians and the sceptics, according to their view as to whether truth can be found. The first group says yes, the second no, and the sceptics are still looking, although Leibniz treats their view sometimes as though they are saying that truth cannot be found.
Leibniz starts by considering the sceptic view that for any claim a counterclaim can be advanced, and that they each have an equivalent value unless some true criterion can be established. Leibniz denies that this sort of equivalence is the case and claims that serious investigation will show that one side or the other has more support. Olaso pointed out that Leibniz took the sceptical claim to be about reasons for views and not just views themselves. Leibniz suggests that in the beginning the reasons are of equal value, later a new reason is discovered and the equilibrium is shattered, but then again another reason is discovered, contrary to the last, and the equilibrium is restored. Leibniz thought he could prove that the invariable equivalence of affirmation and denial is impossible.54
Leibniz questions whether the sceptic goal of achieving ataraxia (quietude) can be achieved by balancing equivalences and resting in doubt. Leibniz portrays doubt as a mental state that causes disturbances because of the uncertainty involved. Real quietude, his insists, can only occur if one has found true knowledge.55
Leibniz’s examination of Sextus’ account of perceptual differences involves seeing the sceptic case as one of giving reasons for questioning whether perceptions are real things or not. He then challenges the results of sceptical analysis and contends that since the sceptics cannot tell real perceptions from others, they can never achieve quietude. He believes that many of the problems raised in the ten tropes are solvable by reasonable analysis of what we perceive and how we judge it by ordinary scientific standards. Leibniz points out that Sextus’ account of how sceptics act seems to presume that the sceptic has reasons for choosing one set of phenomena over another, and hence action seems to be contrary to doubt.56
Leibniz thinks that the ten tropes of Aenesidemus can be resolved by applying hypothetico-deductive method to the problems involved. Leibniz also offers a quick answer to the arguments of Agrippa and contends that one cannot develop a circular reasoning problem over how to judge sensations by reason and reason by sensations. Reasoning has a higher status and so cannot be brought in question by sensations.
The rest of Leibniz’s fragment briefly summarized the continuation of book 1. Leibniz suggests that someone else should follow up on his attacks and proceed to develop a full argument to the sceptics.
Leibniz’s Specimen is the only case we have of a leading philosopher directly trying to answer Sextus. It shows how, from Leibniz’s perspective, he would deal with the points raised by the sceptics, but I doubt that Sextus would be too impressed. In any case, Leibniz’s actual answer to scepticism, in the form of the Specimen, had no influence at the time since it had not been published or, as far as we can tell, was not shown to anybody. So his main contact with and answer to the sceptics comes out more in his conversation and answers to Foucher, Huet, and Bayle.
Besides a long concern with sceptical arguments and with sceptics, Leibniz was interested in the application of some of the sceptical problems to other domains. One that became important at the end of the seventeenth century was the application of Pyrrhonian arguments to historical research. Bible scholars’ attempts to establish accurate chronologies of ancient times and attempts to sort out accurate from inaccurate chronicles, led to some doubts as to whether a true history could ever be found. Pierre Bayle’s Historical and Critical Dictionary began as an attempt to eliminate errors in previous histories. Bayle’s questioning of sources, leading historians, and leading interpretations to historical events led some to what became known as historical Pyrrhonism. In the article “Zueris” in the Dictionnaire, Bayle discussed the question of whether one could be sure of an event that took place seventy-two hours earlier than it was reported. The particular case he dealt with was that it was reported that his main opponent Pierre Jurieu had said in a church in Rotterdam that God commanded us to hate our enemies. Three days later, after many complaints, Jurieu denied that he had made the statement. There were a thousand auditors to the event. Bayle questioned whether one could ever resolve what had happened in the past, when one found any conflicting testimony.
A further impetus to historical Pyrrhonism was the claim by Father Jean Hardouin that all historical documents, with the possible exception of Tacitus, were medieval forgeries done by monks in the thirteenth and fourteenth centuries. Arguments against this claim revealed the difficulty of refuting even such an extreme and unlikely thesis.
Leibniz, who himself was a historian and had written the history of the House of Braunschweig, was interested in efforts to refute historical Pyrrhonism. A German scholar, Bierling, wrote a refutation in 1707, which Leibniz read and congratulated the author on. Leibniz’s own position was that there was no need to question sources when there were no conflicting ones and that one could reasonably be assured of certain data when sufficient examination had been made. Historical research need not end in increasing doubts but could give us more assurance about our beliefs. He admired Bishop Huet’s use of history to try and show the superiority of Christian belief over other religious beliefs, and he hoped this could be a model for studying of other historical developments.
Throughout the seventeenth century, information about China and Chinese civilization, which was emanating from the Jesuit missions there, was creating other kinds of scepticism. Chinese chronology seemed to be older than biblical chronology. The earliest recorded Chinese king supposedly lived many centuries before Noah! And China did not seem to have any connection with the world described in the Bible. The polygenetic thesis put forth by Isaac La Peyrère was offered as a way of accounting for China’s independent development from biblical events. Others tried to find evidence that ancient Chinese figures were really Moses and various patriarchs. The controversies about Chinese chronology and Chinese history versus biblical chronology and biblical history led Pascal to say, “Which should I believe, China or Moses?” Presumably, if one believed China, then scepticism about the authenticity of the Bible would result.
A second major sceptical problem resulting from European information about China was the picture, offered by the Jesuit missionaries, that Chinese society had no religious foundation and that it was operating very well without any religious structures or institutions. In fact, it was, as Pierre Bayle described it, a society of atheists—millions of them—who seemed to be living civilized and honorable lives. This seemed to cast doubt on the need for any religious basis for morality if so large a society as China could operate without religion. This was reinforced by the presentations of Confucius’ thought in Latin and then a French translation by Leibniz’s friend, the abbé Foucher. Confucianism was seen as moral precepts based on human nature alone. Various European thinkers tried to figure out the precise meaning of the Chinese concept of li. Malebranche and Bayle both thought that this concept, which described the basic feature of the world, was a kind of materialism, very much like Spinoza’s one substance, and in fact, more or less identified Spinozism in Chinese philosophy. In contrast, Leibniz sought to avoid the suggestion that Chinese thought conflicted with and cast doubt on European Christian philosophy.
Leibniz had been interested in various accounts from China and took the initiative himself in starting a correspondence with one of the Jesuit fathers who had returned from the Catholic mission to China, Father Bouvet. Leibniz sought information that might help to understand what the Chinese worldview really amounted to. He was quite excited when they figured out that the Chinese hexagons from the I Ching corresponded to binary arithmetic. At the end of his life, Leibniz completed his interpretation of Chinese thought in his “ Discourse on the Natural Theology of the Chinese” (1716). He found, counter to Bayle and Malebranche, that Chinese philosophy was much like the preestablished harmony theory of Leibniz himself. The Chinese conception of Nature was compatible with a world of monads acting in preestablished roles that had been set up by a governing rational divine force. Leibniz hoped by this interpretation of China to remove any sceptical threat by the comparison of Chinese and European thought. He also hoped that seeing Chinese thought as he did would allow for a universal conception of human beings functioning in a natural political society and that the same rational forces that could make Chinese society so effective without need of a superstructure could also lead the Chinese to have a similar morality to that of the rest of mankind. The Chinese world was not atheistic but was a natural rational one. If Christianity were added to it, there would be a model for all mankind.57
To conclude, Ezequiel Olaso, who discovered the Leibniz Specimen and who brooded many years over Leibniz’s contact with the sceptics of his day, offered the following evaluation of Leibniz’s relation to scepticism and to sceptics.
If scepticism is conceived of as a doctrine consisting of a number of propositions abstracted from their own historical context and apart from its role in polemic or dialectic, it is for Leibniz a doctrine which seemingly adds nothing to the Platonic legacy. In the same way, if Leibniz’ doctrine be conceived of as consisting of a group of propositions derived by a process of deduction from indisputable principles, such doctrine will be in no way related to scepticism. Indeed, one may demonstrate demonstrable things without even mentioning those that are doubtful. Hence, from this point of view, which I fear is the usual one, Leibniz and scepticism are two great matters which have little or nothing in common.
However, if we complement such point of view with another, which sees philosophy and science as being two works wrought by men in given social, psychological and historical circumstances, we are better placed to understand the high regard in which Leibniz always held scepticism. Indeed, thanks to the objections of the sceptics men find themselves obliged to do something which they would probably not have done if left to their own devices, that is, go back to first principles, propound definitive justifications, lay sound foundations for science, and thus perfect it. In this sense scepticism represents, for Leibniz, an original approach in the history of philosophy. On the other hand, if Leibniz’ philosophy be conceived of as a diachronic labour based upon a given number of suppositions, and taking shape as it deals with different problems, and exchanges ideas with extant philosophies, it is not difficult to stress the important part played by scepticism in the genesis of that philosophy. It is by the light of the sceptical challenge that Leibniz broke away from tradition and struck out for himself.58
Whether serious or not, for Leibniz one principle joy of his controversies with the sceptics was the fun of a good intellectual fight, with the clever sceptics offering ingenious objections and Leibniz battling to solve their puzzles.
The long interchange between Leibniz and the French sceptics remains rather curious, and its character is no doubt due to the character of both Leibniz’s views and his personality. Since he was not one of those seeking absolutely, immutable, certain truths, he did not have to engage in a life-and-death struggle to slay the sceptical dragon. Hence his interchanges with Foucher, Huet, and Bayle produced not arguments on the very foundations of human understanding, since Leibniz accepted most of the sceptical limitations on human knowledge, but rather clarifications of what sort of knowledge one could have within these limitations and what sort of consistent metaphysical hypothesis could be offered to explain this knowledge. The exchanges with the sceptics led Leibniz to many of his best formulations of his theory, and provided him with the opportunity of exploring various ramifications of his hypothesis. But unlike Descartes and Berkeley, who may best be understood in terms of their heroic and ingenious efforts to conquer scepticism, Leibniz appears, among the sceptics, as a man who has found a happy home among some friends with whom he belongs only in a somewhat superficial sense. Leibniz is neither sufficiently dogmatic nor sufficiently destructive to be engaged in la crise pyrrhonienne. He has accepted both enough doubts and his faith in the unquestionability of the world of rationality so that he can be in neither camp nor need either camp. (Perhaps Bayle’s bon mot about himself really applies more to Leibniz—”I know too much to be a sceptic and too little to be a dogmatist.”)59 But Leibniz was enough of a dialectician to need the sceptics to supply him with food for thought. Thus the relationship of Leibniz and the sceptics may not have been a profound one, but it provided the catalyst for bringing to fruition the ideas teeming within the soul of the great German philosopher. Without the irritation of the sceptics, Leibniz might have published nothing of his system, for without them his intellectual life might have been too uninspiring to encourage him to develop and expound a brilliant new metaphysical hypothesis.