Legend adds that when ordered by the attendant priests to ask God's mercy, Vanini replied that if there were a God he would ask him to blast with lightning the unjust Parlement of Toulouse, and if there were a devil he would ask him to submerge the Parlement in hell; but that since neither existed, he could pray to neither. That this is legend is attested by the fact that a reading of Vanini's work (and few of his many virulent detractors then and during the remaining decades of the seventeenth century bothered to do so) shows that he was not in fact an atheist, but held that there had to be a Necessary Being as the ground of existence for contingent beings, and that this being must further be an Absolute Being capable of resolving all contradictions within itself, since the universe is full of contradictions requiring resolution. Such views might not satisfy orthodox notions derived from revealed religion, but they certainly do not constitute atheism.7
The wild chorus of condemnation, vilification and horror that rose around Vanini's name took its cue from the violent assault mounted by Garasse, whose criticisms were entirely ad hominem and not at all concerned with Vanini's ideas. A more considered engagement with those ideas came shortly afterwards from a more considered pen: that of Descartes' friend and colleague Marin Mersenne, in his L'Impiete des Deistes.8But Mersenne's response to the anxieties prompted by intellectual radicalism was not heeded as much as the frantic propaganda exemplified by Garasse.
As a result of the Vanini affair, a mood set in which well expressed the fear of the old world at what the dawning new world was doing to established certainties.Vanini's execution was the first step; it was followed by several high profile and much discussed further attacks on heterodoxy. One was the 1622 execution in Paris of Jean Fontanier, an occultist who taught mystic doctrines he had learned while travelling in the East. In 1623 the poet Theophile de Viau was accused of atheism. He was tortured and condemned to death, but in 1625 his sentence was commuted to banishment, no doubt because he was well-connected and much admired among Paris's cognoscenti. He died a year later, aged only thirty-six.
The fact that the proximate cause of de Viau's arrest and trial was the "obscene" poetry he had published in Le Parnasse satirique, together with suspicions of homosexuality, should not be taken to suggest that charges of atheism were polite masks for attacks on obscenity and homosexuality. Rather, the latter were taken to be expressive of atheism, or identical with it. For how—so the reasoning went—could anyone soil his hands with either if he were a person of orthodox faith? "Atheism" was a capacious term, in effect meaning heterodoxy in avowed beliefs, or noticeable practice, or both. As always, silence and discretion were safeguards, though not infallible ones; and Descartes was assiduous in maintaining both when it came to tricky matters, but vociferous in proclaiming his orthodoxy when opportunity offered.
The event that most closely touched Descartes, however, was the celebrated banning by the Parlement of Paris of a debate about Aristotelianism. Three of the city's leading "erudite sceptics," Antoine Villon, Jean Bitauld and Etienne de Claves, proposed to debate fourteen atomistic theses and, in the course of doing so, to refute Aristotelianism not merely by argument but by the demonstration of chemical experiments. Since "Aristotelianism" meant the old world, orthodoxy, established dogma, indeed everything to which the new philosophy was opposed both in substance and method, the challenge was a bold one.
The meeting, scheduled for August 1624, stirred enormous interest, and an audience of nearly a thousand was expected at the demonstration. But the Paris Parlement banned the meeting, and its three organisers were banished from the city on pain of death. A few weeks later, on 4 September 1624, the Parlement issued a decree, having taken advice from the Sorbonne's Faculty of Theology, outlawing under penalty of death the teaching of any views "contrary to the ancient approved authors, and from holding any public debates other than those approved by the Doctors of the Theology Faculty."9
This event was associated in the minds both of the public and the authorities with the Rosicrucian scare recently in full spate, and with the contemporaneous publication of Robert Fludd's works in Paris. Fludd was an English physician and alchemist who wrote prolifically, advancing a theory of the creation which started with an account of the macrocosm's emergence from the abyss and the emergence, in turn, of man as microcosm—man in his own turn being macrocosm to the microcosms of his own body's constituent cells, each of which is in turn a macrocosm to a yet smaller microcosm— and so on until the cycles of creation have reached their completion. His works were dedicated to the Brothers of the Rosy Cross, and his closest associate was Michael Meier, who explicitly claimed to be a Rosicrucian. Naturally enough, the works of this famous Hermetic master, regarded with awe and not a little suspicion in his own native England, caused an anxious stir in France, which is why Mersenne undertook to write against them.
Mersenne charged Fludd with heresy, atheism, and the practice of magic. He did not castigate Fludd for alchemical investigations, but argued that those should be confined to the domain of science and kept strictly separate from theology—a particularly interesting view, given what Descartes' philosophy later made possible: namely, the legitimation of scientific enquiry by allowing the safe separation of science from theology, thereby doing much—indeed, single-handedly the most done by any seventeenth-century thinker—to free science from theological interference.
Mersenne had many other worries about Fludd's views. For one thing, he thought they implied a demotion of Christ to the angelic world, and for another he especially disliked Fludd's concept of the "anima mundi," the world soul, and the notion that individual souls "whether of man or brutes" were sparks struck from it. Fludd replied to Mersenne in print, and a debate unfolded between them which for years riveted the attention of all literate Europe.10
For present purposes the interest of Mersenne's wrestling match with Fludd is that it represented a subtle defence of serious enquiry, not only from the fanciful extremes of "magia, cabala, alchymia" but also from the reactionary attitudes of authority and orthodox religion. The danger was that if "magia, cabala, alchymia" provoked too great a crackdown from the temporal and ecclesiastical powers, each equally threatened by the fearful implications of unorthodoxy, then legitimate science would suffer too; so it was necessary to keep a space open for the latter, and to protect its credentials from being tainted by the former. Mersenne and his contemporaries in the serious sciences were performing a delicate balancing act, fending off opposing threats while trying to protect their own work from attracting the wrong kind of attention from a nervous Parlement, court and church.
This endeavour was largely successful. The "erudite sceptics" succeeded in effecting the break with tradition that was required for enquiry in the new sciences to blossom. Many of the leading lights were materialists, atomists, deists or even atheists, but some had high connections at court and most were sensible enough to keep their opinions quiet outside the elite intellectual circle of libertinage erudite that they collectively formed.
Descartes was not a sceptic in the way that Gabriel Naude and La Mothe Le Vayer were, but he was certainly erudite, and because Mersenne and Mydorge had advertised his intellectual virtues to their circle before he returned to Paris, he was soon a member of it and much sought after—as he told his brother in a letter (now lost but quoted by Baillet) written in July 1626. That reputation was built on what Mersenne and Mydorge had learned of Descartes' work and views since their acquaintance with him began properly in 1623. At about that time he had been busy putting together a book discussing the geometry of solid figures, among other things exploring the problem of how to extend the treatment of plane (two-dimensional) figures to three-dimensional ones. By 1625 he had begun to turn his attention to other mathematical problems and to optics, again clearly in ways that excited the admiration of Mersenne and the "erudites." And rightly so, for at about this time Descartes made an important scientific breakthrough: he discovered the law of refraction.
This is the law th
at gives a geometrical description of the behaviour of rays of light as they pass through the interface between one optical medium and another. In fact, the law had twice been discovered earlier: in 1601 by the English astronomer and mathematician Thomas Harriot, and in 1621 by Wilhbrord Snell, professor of mathematics at the University of Leiden. Harriot and Snell did not publish their respective discoveries; Harriot's work has only recently come to be appreciated from a study of his manuscripts, while Snell had better fortune in having his priority over Descartes recognised by Huygens in the 1690s. The law of refraction is now known as Snell's Law as a result. But Descartes, apart from discovering it independently, first gave it a published mathematical description. That publication had to wait more than ten years, however; it did not see print until Descartes included it in the "Dioptric" essay in his Discourse on Method in 1637.
Descartes' discovery of the law resulted from the intensive experimental work he did with Mydorge,Villebressieu, and an instrument-maker called Guillaume Ferrier, in the mid-1620s in Paris. One of their chief interests concerned how to shape a lens so that it would collect parallel rays of light into a single focus, thus overcoming the vexing problems of distortion suffered by refracting telescopes. Scholars attempting to understand how Descartes arrived at the law of refraction are puzzled by the fact that in his 1637 publication of it, his demonstration was inadequate, so they have sought to identify some other route by which he derived it.11
Even more significantly for his later thought, Descartes returned at this time to the subject that had preoccupied him following his "day of discoveries and night of dreams" in 1619, namely, the question of method—and in particular, the identification and statement of rules for conducting effective enquiry. He did not finish the book; and the portion of it that he wrote down was not published until thirty-four years after his death, appearing in Dutch in 1684, and in Latin (the medium for reaching a far wider readership) only in 1701. The book, incomplete and brief, came to be called Rules for the Direction of the Mind (Regulae ad Directionem Ingenii).12
Descartes' aim in the Rules was to give clear and useful directions for achieving success in the search for truth. The original plan was for a work in three parts, each containing twelve rules. In the event, only the first set of twelve rules was completed; the second set stops at rule eighteen, with just the headings for rules nineteen to twenty-one to follow; and there is no third set. The second set deals chiefly with mathematical enquiry, and the projected third set was planned to deal with the empirical sciences. The first set concerns cognition in general, starting from the premise that the aim of study should be to arrive at truth, and proceeding to state how that is to be done.
We should, Descartes said, investigate only those objects that we certainly and indubitably grasp, and moreover grasp for ourselves; and we must accept that we need a proper method for doing so, one which involves ordering and arranging our objects of study carefully, reducing complicated matters to their simplest parts, and beginning our enquiries from these latter in a clear step-by-step manner. This allows us to see everything in a single sweep of thought, grasping all the relevant connections, and keeping it all under constant review. We must stop when we reach difficulties, which will not be the result of our inadequacies (if we have followed the preceding rules properly), but will be intrinsic to the subject itself. Locating the point at which a particular problem becomes unsolvable is itself an important discovery. Concentrating on the easiest matters will give us the habit of seeing the truth clearly and distinctly; methodically reviewing the discoveries of others will exercise our intelligence; continually reviewing what we have learned will make our knowledge more certain and will greatly increase our mental capacity. And finally, we must make use of all the aids provided by reason, imagination, sensory perception, and memory, so that we grasp simple propositions distinctly, bring what we already know into the correct relation with what we are investigating, and identify what must be compared with what, so that we make the best use of our intellectual powers.13
That is what the first twelve rules said in sum, and although they constitute good advice, and in the process raise a number of philosophically interesting points which closer study of Descartes' philosophy brings out, they are hardly an infallible recipe for the discovery of truth—which is what Descartes was specifically eager to provide. Without doubt they were rules he found personally useful, as a way of disciplining his enquiries and reminding him always to work incrementally from one simple and clear proposition to the next, limiting each advance to small steps, leaving nothing out and constantly reviewing every stage, thus placing reliance only on what he was sure was right. But this characterisation of right method is highly general, and is limited even in its theoretical use.
Descartes was of course hoping to contribute to one of the greatest concerns of his time, which was the discovery of methods of enquiry that would exclude nonsense and guarantee genuine knowledge as their outcome. He and Francis Bacon (the latter in his Novum Organon and The Advancement of Learning) stand out as theorists of method because their other work keeps their methodological theories alive; but they were not alone in the quest for this grail. Hermeticists and Rosicrucians shared the desire to discover methods that would unify all knowledge and enable a practitioner to discover anything and everything, moving from discoveries in one region of thought to discoveries in another by infallible means. This was what Descartes and Bacon sought too. But they hoped to arrive at responsible knowledge of the world—a grasp of truth— rather than mystical insights and magical powers.
In the background of Descartes' thinking about method was an emerging general philosophy of nature which owed much to the influence of his friend Mersenne. In the mid-1620s Mersenne published two books setting out his philosophical and scientific views, the Questiones celeberrimae and the Observationes et emenda-tiones. In them he sought to carry out the task described in connection with his controversy with Fludd: to show how to uphold orthodox Catholicism while at the same time defending a mechanistic conception of nature in opposition to the threats both of scepticism and Renaissance occultism. Scepticism denied the possibility of secure knowledge; Renaissance occultism claimed to attain it by magic and arcane practices. As noted, religious orthodoxy was affronted and alarmed by both these challenges, and was too ready to lump both of them together as menaces, and to classify responsible scientific enquiry along with them. That is why Mersenne further sought to show that religious orthodoxy was not called into question by treating the realm of nature as a mechanism whose laws could be discovered by experiment and described by mathematics. This was to be done by distinguishing between what must properly be understood in supernatural terms—the things that pertain to religion—and those that must be understood in natural terms—the things that pertain to the sublunary world. One of the faults he diagnosed in Renaissance occultism was precisely that it attempted to explain the natural world in terms of supernatural properties and powers that were other than those that belonged to God.
Mersenne wrote copiously on mathematics, mechanics, music, acoustics and optics, and offered genuine insights into all of them. If he had done nothing else, he would figure in the history of science for these contributions alone. But his greatest contribution was as the conduit of philosophical and scientific exchanges in his day, by keeping thinkers in touch with one another or at least with one another's ideas. He was a one-man post-office, abetting the cross-fertilisation of ideas in a period rich in discovery and debate.
In Descartes' case Mersenne's influence was direct. The work Descartes was soon to embark upon shows the marks of Mersenne's recipe for protecting religious orthodoxy while making scientific investigation of the world acceptable. The assumption that Descartes started from in his own mature work—that the natural world could be described as if it were a mechanism operating according to quantifiable laws—was already implicit in the discussions he had had with Beeckman some years earlier, but Mersenne's statement of it, coupled w
ith his views about method and how to use sceptical doubt as the starting point for attaining certainty, provided the foundation for Descartes' later work, and almost certainly prompted him to begin writing the large and ambitious book he entitled The World (Le Monde) in the late 1620s.
The rich intellectual life of 1620s Paris, despite the anxieties of the orthodox and occasional persecutions by the authorities, might seem to have been the perfect environment for embarking on a large project such as Descartes had in mind. Yet suddenly—abruptly, unexpectedly— in late 1628 Descartes left Paris and went to the United Provinces of the free Netherlands. He lived there for almost all the rest of his life; and moreover, he did so in circumstances of partial secrecy, only reluctantly letting his home address be known, and changing his place of residence often. The standard reasons given by the biographers for his quitting Paris and his subsequent puzzling behaviour are, first, that he had come to find social life in Paris too distracting, and desired peace so that he could think and write, and secondly, that he had been encouraged to do so by a great man, Cardinal Berulle, who urged him to delay no longer in writing down his important ideas for the benefit of an expectant world.
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