Another way of meeting the sceptical crisis was the formulation of a theory that could accept the full force of the sceptical attack on the possibility of human knowledge, in the sense of necessary truths about the nature of reality, and yet allow for the possibility of knowledge in a lesser sense, as convincing or probable truths about appearances. This type of view, which has become what many philosophers today consider the scientific outlook, was first presented in the seventeenth century in Father Marin Mersenne’s grandiose attack on Pyrrhonism, La Verité des Sciences, contre les Septiques ou Pyrrhoniens, and later, in a more systematic form, by Mersenne’s good friend Father Pierre Gassendi. In such other writers as the English theologian Chillingworth and the French Franciscan writer Du Bosc, one finds the quest for, and a partial statement of, this mitigated scepticism. This attempt to find a via media between the completely destructive tendency of the nouveau pyrrhonisme and a questionable dogmatism has ultimately become a crucial part of modern philosophy, in the movements of pragmatism and positivism. But even though the most theoretical formulations of this mitigated or constructive scepticism probably occurred in the early seventeenth century, a new dogmatism had to develop and be demolished before this new solution to la crise pyrrhonienne could be accepted. Only after the presentation of this view by David Hume, and the digestion of it by Mill and Comte in the nineteenth century, could it become philosophically respectable.
Marin Mersenne (1588–1648) was one of the most important figures in the history of modern thought, and he has been, until very recently, most neglected and misunderstood.1 He is remembered principally because of his friendship and correspondence with Descartes and has usually been classified as a bigoted religious thinker whose saving grace was his friendships, not his ideas. However, this picture hardly corresponds with Mersenne’s vital role in the scientific revolution of the seventeenth century.
He was one of the first students to be trained at the Jesuit college at La Flèche, which Descartes attended in a later class. The training both at La Flèche and the Jesuit college at Caen apparently included a kind of sceptical Aristotelianism; that is, much of the Aristotelian theory of knowledge was presented without any essences. This was probably coupled with a probabilistic theory of knowledge taken over from Cicero’s Academica.2 A view somewhat like this was being discussed in late sixteenth-century English thought. In the works of Richard Hooker some versions of this modified Aristotelianism come up. After this, Mersenne entered the order of the Minimes and became a model of Christian piety and wisdom. His literary career commenced in the third decade of the seventeenth century, with the publication of a group of vast polemical works against every conceivable enemy of science and religion—the atheists, the deists, the alchemists, the Renaissance naturalists, the kabbalists, and the Pyrrhonists.3 After this start, Mersenne devoted the rest of his life to the more constructive task of propagandizing for the “new science,” exhibiting his love of God through his monumental service to the scientific revolution. He was a man with a voracious interest in scientific and pseudoscientific questions, ranging from complex problems in physics and mathematics, Hebrew philology, and music theory to such problems as “How high was Jacob’s ladder?” and “Why do wise men earn less money than fools?”4 Mersenne published a large number of summaries, explanations, and systems of scientific works, including those of Galileo. He also aided and abetted all the leading workers in the “new philosophy,” including, besides Descartes: Gassendi, Galileo, Hobbes, Campanella, Herbert of Cherbury, the superheretic Isaac La Peyrère, and many others. His immense correspondence, which was not published until the twentieth century, encouraged and informed scientists everywhere.5 All in all, Mersenne probably contributed more than any other of his contemporaries to increasing knowledge of, and interest in, the tremendous scientific achievements of the age.
The part of Mersenne’s contribution that will be of concern here is the new understanding that he worked out of the significance of scientific knowledge, and the importance of this in light of the sceptical crisis of the time. The last of Mersenne’s huge polemics, La Verité des Sciences contre les Septiques ou Pyrrhoniens (1625), attempts to answer the Pyrrhonian arguments, but to answer them in a new way. What Mersenne wanted to establish was that even if the claims of the sceptics could not be refuted, nonetheless we could have a type of knowledge that is not open to question and is all that is requisite for our purposes in this life. This kind of knowledge is not that which previous dogmatic philosophers had sought, knowledge of the real nature of things. Rather it consists of information about appearances, and hypotheses and predictions about the connections of events and the future course of experience. Scientific and mathematical knowledge for Mersenne did not yield information about some transcendent reality, nor was it based on any metaphysical truths about the nature of the universe. A positivistic-pragmatic conception of knowledge was set forth that omitted any search for rational grounds for what is known and denied that such a search could be successful yet insisted, against the destructive force of complete Pyrrhonism, that scientific and mathematical knowledge could not seriously be doubted.6
La Verité des Sciences, a work of over a thousand pages, begins, as has been indicated earlier, in the style of Garasse. In the dedicatory letter to the king’s brother, Mersenne denounces the sceptics in quite extreme terms. They are accused of all sorts of shameful and dangerous views and intentions.7 Then, in the preface, further charges are made, culminating in the claim that the sceptics are those libertins who are afraid to show their real impiety. They, therefore, try to convince everyone that nothing is certain in order to attack indirectly the sciences, religion, and morality. Mersenne’s purpose in presenting his huge volume was to put a stop to the impetuous course of Pyrrhonism.8 Any sceptic who reads it will see “that there are many things in the sciences which are true, and that it is necessary to give up Pyrrhonism if one does not want to lose his judgment and his reason.”9
The book itself consists of a discussion between an alchemist, a sceptic, and a Christian philosopher, in which both the Pyrrhonist and the alchemist get their just deserts. The stage is set when the alchemist declares that alchemy is the perfect science. The sceptic offers a rebuttal, first by criticizing the claims of the alchemist and then by presenting an argument for complete scepticism, not solely about the merits of this particular claim to true knowledge but also about the possibility of there being any means whereby human beings can gain knowledge about the real nature of things. A brief general summary of the classical Pyrrhonian case is presented, directed against both Platonic and Aristotelian philosophies. We are unable to know the real essence of things, or the Platonic Forms. All we are ever acquainted with are effects, appearances, and never the ultimate causes or real natures. The causes can be traced back ad infinitum, without ever arriving at the object of knowledge, and unless we find out the ultimate causes, we can never actually comprehend even the particular experiences that we are confronted with.10
Having allowed the sceptic the first general formulation of his case, Mersenne stepped in, in the character of the Christian philosopher, to give his initial presentation of his type of answer to Pyrrhonism. First of all (he said), the problem raised by the sceptic does not show that nothing can be known, but rather that only a few things, the effects, can be known. If our knowledge is really so restricted, it still has some value of a pragmatic variety, since “this little knowledge suffices to serve as a guide in our actions.”11 In order to get along in this world, knowledge of effects is sufficient, since it enables us to distinguish objects, and so on. The point being made constitutes the general pattern of Mersenne’s answer throughout. The sceptical arguments show there are some things we cannot know—namely the real natures of things that previous philosophers have sought to comprehend. However, in spite of the fact that this sort of metaphysical basis cannot be found, we can know something about appearances or effects, namely how to manage in the world of shadows. The sort of knowledge that Plato, Aristotle, Democritus and some others have claimed to possess, Mersenne was willing to concede, cannot be known. But just the same, he maintained, there is a kind of knowledge, radically different, that we do have and that is adequate for our needs in this world.12
Thus, the problems of sense variations and illusions that the sceptics developed at such length may well show that we are unable to know things-in-themselves. Nevertheless, the information about how our experiences differ under different conditions allows us to formulate certain laws about sense observations, for example the laws of refraction. With such laws about appearances we can correct or account for certain sense information and hence eliminate any problems about illusions.13 (It is interesting that Mersenne seems to have been the first one to see that the classical Pyrrhonian claims about the differences between animal experience and human experience are inconclusive since animals do not communicate with us to tell us what they perceive.)14 In the case of all the reports about variations in religious and moral behavior, Mersenne insisted that since we know both divine and natural rules of conduct, it does not matter how other people and cultures behave.15
In general, Mersenne tried to make out the claim that in every field of human interest some things are known, like “The whole is greater than the part,” “The light at noon is greater than that of the stars,” “There is a world,” “It is not possible for the same thing to both have and not have the same property,” “Evil should be avoided,” and so on. There may be no philosophical refutation of the sceptical arguments, but there are a great many things that are not in doubt. If one is reasonable about matters, one will realize that something is known, and one will be happy. If not, one will become completely miserable. One may go so far as to doubt the obvious rules of morality and become a libertin, which leads “headlong into hell with all of the Devils to be burned forever.”16
After taking time out to attack alchemy, Mersenne returned to his war against Pyrrhonism and developed his general criticism in the form of a detailed commentary and refutation of the Hypotyposes of Sextus Empiricus, dealing with almost all of the first book and part of the second. The ten tropes were each presented and answered by pointing out that there are scientific laws about sense variations, such as the principles of optics, and that in spite of all disagreements and differences of opinions, there is common agreement on some matters. No one doubts that fire is hot or ice is cold or that an elephant is bigger than an ant. Dreams or hallucinations provide no reason for scepticism, since when awake and in sound mental condition, we recognize our dream life for what it is. When the sceptic pointed out that the ten tropes show that we do not know the essences of things, Mersenne’s Christian philosopher shrugged this aside with the comment, “that is not … necessary to establish some truth.”17 In spite of all the difficulties raised by Sextus Empiricus, we do not happen to be in doubt about all matters, and we do have means, like measuring devices, for dealing with some of the troublesome situations that arise. With instruments, and by employing laws that we have discovered about perspective, refraction, the effect of wine on eyesight, and so on, we can avoid being troubled by bent oars, pigeons’ necks, and round towers. By being reasonable, we can find ways of living in spite of all the variations in human behavior. Hence “all of the arguments of the Pyrrhonians are nothing but chicaneries and paralogisms, with which one does not have to amuse oneself very long.”18
The Pyrrhonist is not silenced by this commonsensical rejection of his arguments. But, instead of rebutting, he offers other claims drawn from Sextus, summarizing the remaining portions of book 1, then introducing some of the key arguments from book 2 against the possibility of rational knowledge. Everything is a matter of controversy, and every attempt to establish the truth of a theory leads either to an infinite regress or to circular reasoning. The first point is brushed aside by pointing out that many of the controversies cited by the sceptics depend on what some stupid person has said. But, as Mersenne argued again and again, some matters never are actually disputed. And no infinite regress occurs in explanation because there are some self-evident matters which can be used as maxims upon which to build up scientific knowledge; this, in turn, can be verified by checking experientially the predictions that are made on the basis of what we know.19
The sceptic tries to bolster his case by presenting Sextus’ attack against syllogistic reasoning. In order for a syllogism to be true, its premises must be true. To show that the premises are true, further evidence is required, leading either to an infinite regress or to employing the conclusions as evidence for the premises. Besides, the premises could not be known to be true, unless the conclusion were antecedently known to be true. And, in order to know that the premises imply the conclusion, one would have to show that there is a connection between the former and the latter, and that there is a connection between the connection and the syllogism. If this were not enough, there are also the problems about the criterion. To determine if something has been demonstrated, both a judge and a criterion of judgment are needed. But on what criterion will it be decided who or what is the judge or the criterion? Until all these difficulties are resolved, we cannot know anything but how matters appear to us.20
Mersenne’s reply to this critique of rational knowledge consisted of a pragmatic version of Aristotle’s theory of the proper conditions for obtaining empirical and intellectual knowledge. Without offering any argument, he pointed out that, in fact, man is the judge, and each sense the judge of its own objects. When we see the sunlight at noon, we know it is day, and no arguments about criteria or judges make any difference. If we employ our faculties properly, we will discover genuine maxims that everybody accepts. It is not necessary to show indubitably what the criterion of truth is in order to be sure of these maxims. Without answering the sceptical claims, Mersenne pointed out how, in fact, we decide questions. We use our senses, our rules, and our instruments, and we evaluate them by means of our rational faculties.21
Similarly, the Pyrrhonian objections to syllogistic reasoning can be ignored. It just is not the case that the conclusions constitute some of the evidence for the premises. The former may suggest the latter but never establish them. The evidence for the premises is either an induction from materials other than the conclusion or the self-evidence of the premises. If the sceptic really doubts that there are premises that “ravish” the understanding and lead it to certain conclusions, can he also doubt that he knows that he doubts? If he doubts this, can he doubt that he doubts, and so on? No matter how the sceptic squirms, he will have to admit that something is true, and hence “it is necessary to bid an everlasting farewell to your Pyrrhonism.”22
The halfway house that Mersenne was trying to construct between the sceptical denial that we possess any knowledge and the dogmatic claim that we can know the real nature of things is exhibited in a digression that occurs concerning the merits of Francis Bacon’s proposals. Bacon was accused of going to both extremes. The Idols are just the old sceptical arguments and can be disposed of in a commonsensical, practical way. The positive procedures offered by Bacon for discovering the truth are unworkable. Besides the fact that they are not based on actual scientific method, they fail to take into account our total inability to find the true nature of things. Regarding “whatever phenomena that might be considered in Philosophy, it must not be thought that we could penetrate to the nature of individuals, nor to what takes place inside of them, for our senses, without which the understanding can know nothing, perceive only that which is external.”23
On the other hand, as Mersenne declared in closing the first Book of La Verité des Sciences, brushing aside the Pyrrhonian arguments about physics and metaphysics by pointing out again that there are things we can know and practical ways for dispelling doubts, “One must no longer suspend judgment. We should accept the truth in our understanding, as the ornament and the greatest treasure that it can receive, otherwise it will be in eternal darkness and will have no consolation.”24
If this acceptance of the force of scepticism, and this proposed pragmatic means of resolving doubts, did not suffice to eliminate Pyrrhonism, then Mersenne put forth his ultimate answer to complete scepticism—the vast body of mathematical and physical information that is known. When confronted with this, can one still be in doubt? And so the last eight hundred pages of La Verité des Sciences is a list of what is known in these subjects, matters on which there is no need for suspense of judgment. As arithmetic and geometry are described, along with some odd problems in the philosophy of mathematics, and the “theology” of mathematics, the Pyrrhonist gradually discovers that this body of knowledge is “most excellent for overturning Pyrrhonism which had made me doubt of all things until I had the good fortune to meet you.”25
The type of answer that Mersenne presented to scepticism has been described by Lenoble as similar to Diogenes’ refutation of Zeno by walking around. Pyrrhonism has been rebutted merely by exhibiting what we know.26 But the arguments for complete scepticism have been ignored rather than refuted.27 As Bayle pointed out regarding Diogenes, the appeal to the experience of motion does not constitute an answer to the arguments at issue.28 Nor does the appeal to the knowledge that we obviously possess constitute an answer to the arguments raised by Sextus Empiricus. But Mersenne was only too willing to grant this point. The refutation of Pyrrhonism was intended to stop the destructive side of the humanistic sceptics, those who doubted everything and intended to suspend judgment on all questions. The sciences (considered as the study of phenomenal relationships) and mathematics (considered as the study of hypothetical relationships) have given us a kind of knowledge that is not really in doubt, except by madmen. But the sort of assurances sought by the dogmatic philosophers could never be found for this knowledge. Thus, a fundamental scepticism had to be accepted, a doubt that any certain foundations could ever be uncovered as the grounds for what we know. But this scepticism should not be extended from a doubt concerning foundations or grounds to a doubt concerning the very matters that, regardless of any sceptical arguments, we do in fact know.29
In some of his later writings, when he was not occupied in attacking scepticism, Mersenne made his own “epistemological” or “theoretical” Pyrrhonism quite clear. In Les Questions Théologiques, he argued that a science of eternal truths is not possible, and that the summit of human wisdom is the realization of our own ignorance. Everything we know is open to some doubt, and none of our beliefs can be adequately founded. The wise man recognizes that he knows no subject with sufficient evidence and certainty to be able to establish it as a science, in the sense of a body of indubitable or demonstrable knowledge. “For it can be said that we see only the outside, the surface of nature, without being able to enter inside, and we shall never possess any other science than that of its exterior effects, without being able to find out the reasons for them, and without knowing how they act, until it pleases God to deliver us from this misery, and to open our eyes by means of the light that He reserves for His true admirers.”30
In the Questions inouyes, Mersenne asked, “Can one know anything certain in physics or mathematics?” And he answered that we cannot explain the causes of the most common effects, like the cause of light, and of falling bodies. In fact, we cannot even prove that the world we perceive is not just mere appearance. Thus, “there is nothing certain in physics, or there are so few things certain that it is difficult to state them.”31 In mathematics, the truths are only conditional. If there are objects like triangles, then certain geometrical theorems are true.32
Mersenne’s theoretical Pyrrhonism, plus his vehement opposition to applied scepticism, is brought out further by some comments of his correspondents and friends. They seem to realize that Pyrrhonism is a very trying subject for Mersenne. Pierre Le Loyer, who had earlier written against scepticism, accused Mersenne of this view but carefully softened the blow by adding that he knew that he was definitely not a Pyrrhonist.33 Gassendi, who came to share Mersenne’s “constructive scepticism,” confessed that he, himself, was a sceptic, and that he knew that this annoyed Mersenne. But, Gassendi said, they could compromise, and both live their daily lives on a probabilistic basis.34 La Mothe Le Vayer, “the Christian sceptic,” added a note to Mersenne to his Discours Sceptique sur la Musique, which Mersenne had published as part of one of his own books, in which La Mothe Le Vayer tried to point out the areas of agreement between Mersenne and the nouveaux pyrrhoniens.
I have not made difficulties by playing with you with the ways for suspending judgment, knowing well that you have never disapproved of them within the limits of human knowledge, and that you have never blamed the Sceptic, when respectful towards Heaven, and enslaving his rationality under the obedience of faith, he has been content to attack the pride of the Dogmatists by showing the uncertainty of their disciplines. The same sword can be used by a wicked person to commit an infamous murder, and can be the instrument of an heroic deed in the hands of a virtuous man. He who allows divine matters to be treated in a Pyrrhonian manner is as much to be condemned as another is to be praised for showing that what is set forth as the greatest of worldly wisdom is a kind of folly before God, and that all human knowledge is dependent on dreams of the night.35
La Mothe Le Vayer and Mersenne could agree in using the sceptical sword to slay the dogmatist, but the former wanted to slay the scientist as well. Mersenne accepted the antimetaphysical use of Pyrrhonism, but he also insisted, in spite of all the sceptical doubts, on the truth of the sciences.
A further item in Mersenne’s career illustrates his attitude—his advocacy of Hobbes’ political theory as a cure to destructive Pyrrhonism. In 1646, Mersenne wrote to the archsceptic Samuel Sorbière, telling him that if he examined Hobbes’ De Cive, it would make him renounce his scepticism.36 What Hobbes had discovered, apparently for Mersenne, was a new science, the science of man. If the sceptic saw what could be known in this area, he would no longer advance his doubts, even though it would still be the case that no ultimate grounds could be given for his knowledge, and no knowledge of the real nature of things could be discovered.
Mersenne, unlike Charles Sorel, who borrowed many of Mersenne’s ideas, was offering a peculiarly novel type of solution to the sceptical crisis. He did not contend, as Sorel did, that we can have knowledge of the true nature of things but cannot know everything about reality. Instead, Mersenne’s contention was that, epistemologically, there was no solution to the sceptical crisis. But this did not deny the fact that in practice we do have knowledge, that is, reliable information about the world around us. We may not be able to establish that there really is a world, or that it actually has the properties we experience, but we can develop sciences of appearances that have pragmatic value, and whose laws and findings are not doubtful except in a fundamental epistemological sense. The destructive humanistic sceptic, like La Mothe Le Vayer, who would give up what small guidance we have because of his theoretical doubts, is as much of a fool and a menace as the religious sceptic who gives up Christianity because its doctrines cannot be given an absolutely certain rational foundation.
Mersenne had found an answer to the challenge of the nouveau pyrrhonisme, and an answer that was to have a great history in more recent times. The sceptics had raised apparently insoluble doubts as to our ability to find a certain and indubitable basis for the knowledge we have. Instead of trying to resolve the doubts, Mersenne tried to save the knowledge by showing that its reliability and use did not depend on discovering the grounds of all certainty. Scientific achievements do not depend on some unshakable metaphysical system; therefore, they ought not to be doubted or discarded because of the absence of such a basis. The dogmatist and the destructive sceptic were both wrong, the former for insisting that we can and must have knowledge of reality, the latter for insisting that everything is in doubt. Between the two views lies a new outlook, constructive scepticism, doubting our abilities to find grounds for our knowledge, while accepting and increasing the knowledge itself. Mersenne’s mechanism, his world machine, was not set forth as the true picture of the real world, as it was for his fanatic friend René Descartes, but as a hypothesis for organizing and utilizing our knowledge. Beginning with Mersenne, a new type of scientific outlook had arisen, a science without metaphysics, a science ultimately in doubt but for all practical purposes verifiable and useful.37
Put another way, the sceptical crisis results from showing that the sort of certainty the dogmatic philosophers seek is unattainable, because, in terms of their quest, certain insoluble difficulties can be proposed that prevent the discovery of absolutely true, indubitable knowledge. Thus, as Pascal avowed, as long as there are dogmatists, the sceptics are right. But if one eliminates the dogmatic standards for genuine knowledge, then the Pyrrhonian attack becomes ridiculous, since it is developed in terms of these strong demands or conditions laid down by the dogmatic philosophers.38 As soon as Mersenne had shifted the standards of true knowledge from self-evident, indubitable truths, or true demonstrations from them, to psychologically unquestioned, or even unquestionable, truths (which may be false on the former standards), then the sceptics had lost their opponent, and their attacks, applied to Mersenne’s type of knowledge, became ludicrous and wantonly destructive. The “reasonable” sceptic could abandon his doubts regarding this new conception of knowledge and join Mersenne in his quest for the most convincing, most useful presentation and organization of the information we are all aware of, the development of the picture of the world as a machine.
Pierre Gassendi (1592–1655), a great scientist, a fellow priest, and Mersenne’s best friend, gradually adopted this attitude of “constructive” scepticism and devoted much of his later writings to working out a philosophy midway between total scepticism and dogmatism.39 Gassendi’s atomism was presented, especially in its final form, as the best explanation of the world of appearance. Much more than Mersenne, Gassendi tried to clarify in detail the epistemological status of his mechanical picture of the world through a serious, careful, systematic analysis of the nature of knowledge. His magnum opus, the Syntagma, deals not at all with metaphysics but does treat at great length what his hero, Epicurus, called “canonics”—philosophy of logic and theory of knowledge. Here Gassendi examined the views he had originally espoused, those of the Pyrrhonists, and showed why he was abandoning their total doubt about the possibility of knowledge.
After presenting a careful summary of the sceptical theory as it appears in the writings of Sextus Empiricus,40 Gassendi then, in terms of the problem of knowledge as presented by the Pyrrhonians, tried to defend his own compromise between dogmatism and scepticism. The basic question is: Is there an absolutely certain criterion for distinguishing truth from error? Some things are obvious at certain times, for example “It is day,” while others are not. The sceptics, and everyone else, accept what is evident, or apparent. The problem arises in connection with what Sextus called the nonevident, those things that are hidden from us. Some of these are absolutely nonevident, such as whether the number of stars is odd or even. (This, and most of the illustrations employed by Gassendi in discussing the problem of knowledge, are drawn from Sextus’ analysis of the problem of whether indicative signs exist.) Others are naturally nonevident but can be known by some signs or intermediaries, as, for instance, the existence of pores in the skin can be inferred from the phenomenon of sweat. Finally, there are some things that can be known evidently but, due to temporary conditions, are hidden from us.41
The cases of the naturally nonevident things and the temporarily nonevident ones require some instrument or criterion in order for us to know them. The latter, even the sceptics admit, can be discerned by “suggestive signs,” that is, constantly conjoined phenomena, such that when we perceive one, we think of the other. Thus when we see smoke, we are aware that there is a fire, though it may be temporarily hidden from us. The Pyrrhonists regard this kind of knowledge of the nonevident by means of suggestive signs as valuable in practical life.42 However, there is a complete opposition between the sceptics and the dogmatists concerning the signs by which we may discover the naturally nonevident. The sceptics doubt that there is any criterion and that we can know things other than how they appear to us. The dogmatists insist that the truth of things can be discovered by us through indicative signs.43
Gassendi criticized the dogmatic view because it exaggerated the power of the human mind. The secrets of nature, of things-in-themselves, are forever hidden from us. But, at the same time, the sceptics have also gone too far. A way to knowledge can be found between the two opposing camps. It is obvious that something exists and that some things can be, and are, known. So total doubt is uncalled for. Even the sceptics agree that we are aware of appearances. But, also, we are capable of knowing something about the nature of reality by means of the criteria by which we can discern a type of indicative sign. The senses allow us to know the visible or apparent sign, and our reason enables us to interpret it, and thereby discover the hidden unperceived object. Although the senses are sometimes unreliable and erroneous, by careful reasoning we can correct their errors. The test as to whether we reason rightly and discover true knowledge lies in experience, through verifying predictions. The sceptical quibbles about the value and foundation of reasoning are of no importance, since there are certain unquestioned principles of reasoning that are sufficiently evident to use as a basis for our inferences.44
This answer to scepticism, like Mersenne’s, does not deny the force of Pyrrhonism as applied to the knowledge the dogmatists seek, the knowledge of the true nature of things, “the actual quality that is in the object,”45 and the reasons why objects have these properties. In fact, the very sort of necessary information the Stoics claimed to gain by indicative signs,46 Gassendi and the sceptics believed was unattainable. But Gassendi thought there was a less imposing but still useful type of indicative sign, one that taught us the causes of appearances in scientific terms. From experience, through careful reasoning, we can discover laws or reasons that explain why we have the perceptions we do, why honey seems sweet to us, why we see certain colors.47 In terms of the variations in our experience, we can formulate some truths about the ways objects appear to us under different conditions, laws about the causes of the variations in what we perceive. Gassendi was unwilling to conclude that since we cannot know the essential nature of things, therefore we can know nothing beyond either what appears to us or the observable regularities in these appearances. Between knowledge in the dogmatists’ sense and the appearances and suggestive signs of the Pyrrhonians there exists a level of scientific knowledge. This knowledge is based on a studiously careful scrutiny of appearances, and rational interpretations and explanations of these appearances, not in terms of the nature of the real objects that produce them, but in terms of the conditions that make our experience possible and intelligible. Thus, scientific explanation, which for Gassendi is in terms of an atomic theory, accounts for our experience of sense qualities but does not tell us anything about the nature of things-in-themselves, except how they appear in relation to us. This is the type of scientific object that Gassendi wished to protect from the doubts of the sceptics. We construct or learn about these objects from the indicative signs in experience. We then describe these scientific objects (the atoms) in terms of the qualities found in experience. And, finally, we authenticate this atomic explanation in terms of verifiable predictions about experience.48 Gassendi’s atomism may not have borne much fruit, in terms of scientific discovery or satisfactory scientific explanation, but it was at least a constructive result from his Pyrrhonism, unlike the destructive antiscientific attitude and theory of his good friend La Mothe Le Vayer.49
When Gassendi was confronted with a dogmatic theory, a metaphysical picture of the structure of the universe and our knowledge of it, then the Pyrrhonian basis of his thought came out clearly and sharply, not as a disguised equivalent of scepticism, as it did in Mersenne, but as a blunt avowal of complete epistemological Pyrrhonism. Thus, when considering the views of Aristotle, Herbert of Cherbury, Descartes, or even the mathematical physicists, whom he took to be Platonists or Pythagoreans, Gassendi advocated total scepticism about the world beyond appearance. His earliest work, directed against Aristotle, concluded: nihil sciri.50 His comments on Herbert’s De Veritate, both to the author and to their mutual friend Diodati, again assert this fundamental Pyrrhonism. “The truth, in my view, is well-hidden from the eyes of men and Monsieur Herbert seems to me to have gone a little too fast and to have had a bit too high an opinion of his view when he so indecently condemned the arguments of the Sceptics.”51 Gassendi explained to Herbert that like the sceptics, he, Gassendi, knew only about such appearances as the sweet taste of honey, and could explain these in terms of natural, experiential qualities. But beyond this, unfortunately, we can never and will never know the truths of reality. Those who claim to uncover these ultimate verities failed to convince him. “But, concerning what you think to be the truth of the thing, or the intimate nature of honey, this is what I ardently desire to know, and what remains still hidden for me, despite the almost infinite number of books which have been published up to the present with the pretention of communicating to us, what they call, a demonstrative science.”52 Similarly, his vast writing on Descartes—the Fifth Objections, the Institutio, and the comments on the logic of Descartes in the Syntagma —all stress first the obviousness of the sceptical side of the Meditations, that is of the First Meditation, and next that the positive side of Descartes’ theory, its claim to true knowledge of reality, is grossly exaggerated and really leads only to a most dubious view. If we try to obtain true knowledge of things solely from the clear and distinct ideas in our understanding, Gassendi insisted, we are always liable to error, since what seems clear and distinct to us at one time may not appear so later. Because of our weakness, we should realize that we can never take adequate precautions to assure ourselves that we have not been deceived when we attempt to build solely on our ideas. Instead, we should turn to nature, to experience, for our guidance, and we should limit our quest for knowledge to what can be discovered on this basis.53
Gassendi’s extreme caution, his constant reliance on experience and tradition, inhibited him as a creative scientific thinker,54 but allowed him to formulate quite fully a scientific outlook devoid of any metaphysical basis, a constructive scepticism that could account for the scientific knowledge that we do, or can, possess, without overstepping the limits on human understanding revealed by the Pyrrhonists. The via media that he and Mersenne developed could supply an adequate rationale for the procedures and discoveries of science, without having to furnish an unshakable foundation for the new edifice of scientific knowledge. Even though Gassendi worked out his new physics in great detail, it probably failed to become the new world-picture and the new ideology partly because of certain limitations in its author’s temperament, a lack of the boldness and audacity that was to characterize such monumental explorers of the new world machine as Galileo and Descartes. Gassendi was extremely conservative, unwilling to leap beyond the experiential information and the intellectual traditions of humankind.55 He was unwilling to break with the qualitative world of ordinary experience or throw overboard the heritage of human wisdom in order to pursue a new insight and a new frame of reference.56 Having less comprehension of the nature of mathematics than did Mersenne, Gassendi was sceptical of the role that it could play in our understanding of nature and feared that the mathematical physicists were a new brand of metaphysicians, trying to portray the real nature of things in mathematical terms, like the Pythagoreans and Platonists of antiquity.57
But, whatever his limitations might have been, Gassendi, perhaps even more than Mersenne, had accomplished one of the more important revolutions of modern times, the separation of science from metaphysics. Building his new outlook on a complete Pyrrhonism with regard to any knowledge of reality, or the nature of things, he was able to develop a method and a system of the sciences that, of all those of the seventeenth century, comes closest to the modern antimetaphysical outlook of the positivists and the pragmatists. Rochot, in his many studies of Gassendi’s atomism and his place in the history of scientific and philosophical thought, shows him to be a most important link between Galileo and Newton, in moving from a conception of the “new science” as the true picture of nature to one wherein it is seen as a hypothetical system based solely on experience, and verified through experience, a conception in which science is never thought of as a way to truth about reality but only about appearance.58
Also it should be mentioned that Gassendi and Mersenne tried valiantly to find an empirically justified astronomical system that could agree with the Church’s pronunciations in the Galileo case. Though they sympathized with Galileo and would have been happy with the heliocentric system, as churchmen they accepted the Church’s right to declare what is acceptable on the subject. They kept trying to develop an astronomy somewhere between that of Tycho and Galileo.59
Many have counted Gassendi as a secret atheist. He sought to separate his sceptical views from religious beliefs. On the one hand, he offered an empirical theology deriving some knowledge about the deity from what man discovers about the universe. He also explained human knowledge of Christianity as being based, at least at part, on the pictures and statues that people saw in churches and on what they heard in services. Man’s knowledge of God, for him, came mainly from empirical inspection of what happens in the world. Thus, he rejected the sort of ontological theology that permeated Descartes’ view.60 However, he also tried to delimit scientific inquiry from investigating articles of faith. Silvia Murr’s work on Gassendi’s view on the immortality of the soul describes how he did this. It is still open to question whether or not he was sincere. As mentioned earlier, he functioned as a priest all his adult life, and nobody questioned his religion while he was alive.
This attitude of mitigated or constructive scepticism of Mersenne and Gassendi also appears in more embryonic form in some of their contemporaries. The Franciscan writer Jacques Du Bosc, who was, apparently, once a follower of the nouveau pyrrhonisme, found that scepticism was praiseworthy as an antidote to dogmatism but that as a philosophy it was at least as dangerous as what it opposed. What was needed was some in-between view, which he called “l’indifférence.” The Pyrrhonist, “in fleeing from the too much, he has fallen into the too little; in fleeing from the fancy for knowledge, he has fallen into the fancy for ignorance.”61 Du Bosc accepted the sceptic’s critique of traditional philosophy as sound but his conclusion as excessive. The middle ground, “l’indifférence” or “la médiocrité,” is found in a sort of self-analysis, in realizing that we are halfway between the ignorant brutes and the all-knowing angels.62 By a kind of spiritual training, we develop a criterion for discerning intellectual and religious truths.63 Thus, though admitting the full force of the Pyrrhonian barrage, Du Bosc still insisted there was a way to some positive and important knowledge, especially theological and moral. This kind of mitigated scepticism has been analyzed by Julien-Eymard d’Angers as a foreshadowing of the philosophy of Blaise Pascal.64
Mitigated or constructive scepticism represents a new way, possibly the closest to contemporary empirical and pragmatic methods, of dealing with the abyss of doubt that the crisis of the Reformation and the scientific revolution had opened up. (It was novel for its time, though it obviously echoes some of the attitudes of Greek thinkers like Carneades.) For some, the age of Montaigne and of Luther and Calvin had set off a quest for certainty, a search for an absolutely certain foundation for human knowledge. For others, the quest was only for stability, for a way of living once the quest for infallible grounds for knowledge had been abandoned, and for a way of living that could accept both the unanswerable doubts of the nouveaux pyrrhoniens and the unquestioned discoveries of the intellectual new world of the seventeenth century. Mersenne and Gassendi sought to reconcile the sceptical triumph over the dogmatists with the mechanistic triumph over Aristotelianism and Renaissance naturalism. They found such a reconciliation not in a new dogmatism, or a materialistic metaphysic, but in the realization that the doubts propounded by the Pyrrhonists in no way affected la verité des sciences, provided that the sciences were interpreted as hypothetical systems about appearances and not true descriptions of reality, as practical guides to actions and not ultimate information about the true nature of things. La crise pyrrhonienne fundamentally could not be resolved, but, at least, it could be ignored or abided with, if one could relegate the doubts to the problems of dogmatic philosophy, while pursuing scientific knowledge as the guide to practical living. La crise pyrrhonienne would have disastrous consequences if one accepted the conclusion of the destructive humanistic sceptics and extended one’s doubts to science and even religion. But it could have beneficial results were it restricted to the epistemological sphere as a means of eliminating the dogmatists’ hopeless pursuit of absolute certainty, while leaving the scientist or the theologian free to discover truths about appearances.
This attitude of constructive or mitigated scepticism is in sharp contrast to either the new metaphysical views of some of the “new scientists” like Galileo, Campanella, and Descartes or the scientistic attitude that was to develop in the Enlightenment. Although Galileo, Campanella, and Descartes might occasionally assert, for tactical reasons, that their theories were only hypothetical,65 and that there was a level of knowledge about essences that man could never know,66 at the same time they seem to share a conviction that man is capable of attaining true knowledge about the real world, and that the mechanistic picture of the universe is an accurate description of the way nature actually operates. In the view of Galileo and Campanella, God has given us the faculties to attain knowledge of the nature of things. However, our knowledge is only partial, unlike his complete knowledge. Nonetheless, we have no reason to question or doubt what we know, and we have no reason to restrict our knowledge to appearances, rather than reality.67 The sceptical crisis seems to have bypassed these thinkers and left them only with doubts about the Aristotelian quest for certainty and not about the quest itself.
Descartes criticized Galileo for being too modest in his claims and not seeing that the truths of the new science rest on a certain metaphysical foundation that guarantees their applicability to reality, and that provides the complete assurance that separates these discoveries from opinion or probable information. In approving of Galileo’s use of the mathematical method, Descartes commented:
I agree entirely with him in this, and I hold that there is no other means for finding the truth. But it seems to me that he lacks much in that he continually makes digressions, and does not stop to explain a matter completely; which show he has not examined things in an orderly way, and that, without having considered the primary cause of nature, he has only sought the reasons for some particular effects and thus that he has built without a foundation. Now inasmuch as his way of philosophizing is closer to the true one, to that degree can one more easily recognize its faults, just as it can better be ascertained when people go astray who sometimes follow the right road, than when those go astray who have never entered upon it.68
In the case of all three of these thinkers, Galileo, Campanella and Descartes, though there might be some disagreement as to the foundation for the truths of the “new science,” there is no doubt that the “new science” is true, and true about the real nature of the physical world. There is no epistemological Pyrrhonism, but rather a kind of realism. Science is not the constructive issue of complete doubt but a kind of knowledge that is not open to question either on the theoretical or philosophical level.
As Mersenne and Gassendi had seen, the achievements of science in no way disproved Pyrrhonism, unless the sceptic were foolish, or impious enough, to doubt the discoveries of the scientists, as well as the grounds for them. The latter were open to question and had been undermined by the onslaught of the nouveau pyrrhonisme. But the former were as convincing and as reliable as ever. The truth of the sciences is not at issue, but this truth, for the mitigated sceptics, could only be appreciated in terms of la crise pyrrhonienne and not as a rational, philosophical answer to it.
The success of constructive scepticism as the core of the modern empirical and pragmatic outlook, the recognition that absolutely certain grounds could not be given for our knowledge and yet that we possess standards for evaluating the reliability and applicability of what we have found out about the world, had to await the rise and fall of a new dogmatism. Though Mersenne and Gassendi were widely read and approved of in their day, the acceptance of their type of philosophical view as a major outlook did not come until attempts were made to end la crise pyrrhonienne by erecting a new intellectual foundation for human certitude.69 For a time the constructive sceptics were cast into the shadows, while a new metaphysical drama was played out on the center of the stage, while new systems were proposed to give an answer to the sceptical challenge. After new systems like those of Herbert of Cherbury, Jean de Silhon, and René Descartes had met the fate of the older ones, then constructive scepticism could be absorbed into the mainstream of philosophy.