It is not difficult to see why Descartes was in such a positive frame of mind. He had devoted himself to intellectual labours, and there are few things as satisfying as developing ideas and writing about them. The work he was engaged on was his book Le Monde, the aim and contents of which was to give a systematic description of the natural world and man. "But just as painters, not being able to represent all the different sides of a body equally well on a flat canvas, choose one of the main ones and set it facing the light, and shade the others so as to make them stand out only when viewed from the perspective of the chosen side," he wrote, "so too, fearing that I could not put everything I had in mind in my discourse, I undertook to expound fully only what I knew about light. Then, as the opportunity arose, I added something about the sun and the fixed stars, because almost all of it comes from them; the heavens, because they transmit it; the planets, comets, and the earth, because they reflect light; and especially bodies on the earth, because they are coloured, or transparent, or luminous; and finally about man, because he observes these bodies."14 In other words, Descartes arranged his account of the natural universe (of everything other than the spiritual realities of God and the supernatural) by employing the idea of light as the connecting thread; light itself, then its sources, its medium, the things that reflect it, and the thing— man—that observes it.
Le Monde was finished, but never published, at least in its original form. But Descartes excerpted parts of the manuscript for publication a few years later, and the book's two chief components appeared after his death as Traite de la Lumiere and Traite de I'homme. Most of the writing of Le Monde was done at Henry Reneri's home in Deventer in 1632; he wrote from there to Mersenne in June of that year to report progress.15 Prior to this Descartes was busy researching—and not only in astronomy and mathematics, as his university studies show, but also anatomy, so that he could better understand the way animal and human bodies function. In April 1630 he wrote to Mersenne, "my work is going slowly, because I take much more pleasure in acquiring knowledge than in putting into writing the little that I know . . . I am now studying chemistry and anatomy simultaneously . . . the problems in physics that I told you I am addressing are all so connected and mutually dependent that it is not possible for me to solve one of them without solving all of them, and I cannot do that more quickly or briefly than in the treatise I am writing."16 In Amsterdam one of his lodgings was on a street of butchers (doubtless Kalverstraat), and he reported going every day to watch the butchers slaughter animals and to collect anatomical specimens from them to take home and study.
The pleasure Descartes took in the process of researching and writing Le Monde is evident in his letters, which (apart from those addressed to Beeckman during the contretemps) are rich in ideas and technicalities of a mathematical and scientific kind. He showed the mathematical part of his work to Golius, who responded positively, eliciting from Descartes a characteristic reply: "I am very much obliged to you for your favourable judgement on my analysis, for I know very well that the greater part of it is due to your good manners. I have a somewhat better opinion of myself all the same, because I see that you have made a full examination of the facts before passing final judgement on it."17
From the point of view of the history of thought, the deeply significant thing about Descartes' Le Monde is the assumption on which it rests: that the natural world can be examined and understood as a system of matter in motion obeying natural laws, without the need for any invocation of supernatural forces or agencies. This way of thinking about the universe was the seventeenth century's great revolutionary departure, because it premises the idea that even if one believes that the world is created by a deity, nature can be regarded as functioning independently according to its own laws. Just as a watch works by itself once it has been set going by a watchmaker, so the world, once begun, thereafter operates according to mechanical principles without needing the constant supervision and intervention of an external agency. When Descartes put this idea to Mersenne by saying that once the metaphysical question of God's existence and creative agency is settled, the world itself can be treated as a purely material realm, he cautiously added that, of course, this had to be treated as a fable, an "as if"; for he did not wish to impugn the theological doctrine that the existence of a deity is necessary to the world, nor that the account of creation in Genesis is literally true.18 This rider rings hollow, of course, since if the material realm requires only natural laws, the introduction of (literally) a deus ex machina to invent it and get it going is superfluous; but Descartes was anxious that his sincerity in this belief should be taken as unquestionable, and he never wavered in his efforts to soothe religious sensibilities in his letters to Mersenne and others, nor in later trying to get the Jesuits to approve and even adopt his works.
But in the works themselves there is much to make the religiously orthodox uneasy. Once God had given his initiating push to the universe, according to Descartes' principles in Le Monde, the mechanism could run itself for eternity. Stars and planets, and the earth itself, would form from the interactions of swirling matter, and everything else would naturally follow as an outcome of the same laws, even to the emergence of humankind itself. "The laws of nature are sufficient to cause the parts of the chaos [of matter] to disentangle themselves and arrange themselves in such good order that they will have the form of a quite perfect world," Descartes wrote, "a world in which we shall be able to see not only light but also all other things, general as well as particular."19 This of course had to be understood, Descartes repeatedly wrote, "as if" God had decided to create matter and its laws and to allow the latter to operate uninterruptedly on the former; but this of course was just an imaginary and illustrative supposition; "allow your thought to wander beyond this world to view another world," he wrote, "a wholly new one which I shall bring into being before your mind in imaginary spaces . . . we are taking the liberty of fashioning this matter as we fancy . . . let us expressly suppose . . ."20
But if this was intended to mollify the scrutinising officers of the Inquisition, two things Descartes then said would quickly have altered their view. First, he pointed out that his description of how the universe could form according to natural laws was both clear and consistent—the implication being that this was indeed no "as if" at all. "Were I to put into this new world the least thing that is obscure, this obscurity might conceal some hidden contradiction I had not perceived, and hence, without thinking, I might be supposing something impossible. Instead, since everything I propose here can be distinctly imagined, it is certain that even if there were nothing of this sort in the old world, God can nevertheless create it in a new one. For it is certain that he can create everything we can imagine."21
Secondly he insisted that the description was entirely naturalistic, that is, based on scientific principles alone: "Note that by 'nature' I do not mean some goddess or any other sort of imaginary power. Rather, I am using this word to signify matter itself, in so far as I am considering it taken together with all the other qualities I have attributed to it."22
And so Descartes proceeded, describing the "imaginary" world, its laws, its phenomena, and the presence in it of human beings— considered, according to the "imaginary" hypothesis, as a composition of body and soul, in which the body is "nothing but a statue or machine made of earth."23 He gave a full account of the workings of the body—the digestion, the circulation of blood, respiration, the workings of the "animal spirits" which flow through the "cavities of the brain" and the nerves to work the muscles. He drew an analogy with the moving, music-playing and even speaking water-powered statues in the royal gardens of St. Germain in Paris: "Similarly you may have observed in the grottoes and fountains in the royal gardens that the mere force with which the water is driven as it emerges from its source is sufficient to move various machines, and even to make them play certain instruments or utter certain words depending on the various arrangements of the pipes through which the water is conducted."24
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"Indeed," he continued, "one may compare the nerves of the machine I am describing [i.e. the human body] with the pipes in the works in these fountains . . . When a rational soul is present in this machine it will have its principal seat in the brain, and reside there like a fountain-keeper who must be stationed at the tanks to which the fountain's pipes return if he wants to produce, or prevent, or change their movements in some way."25
This part of Descartes' account was based on close anatomical studies. Only human beings had souls, in his view, so it followed that non-human animal bodies were merely machines, devoid of emotion and sensation, and operating simply by stimulus and response. Accordingly, his anatomical studies included vivisection. "If you cut off the end of the heart of a living dog," he wrote, "and insert your finger through the incision into one of the concavities, you will clearly feel that every time the heart shortens, it presses your finger, and stops pressing it every time it lengthens."26 He had what he took to be empirical grounds for thinking that animals were simply stimulus-response mechanisms; in what is the first known observation of the conditioned reflex, he told Mersenne that if you whip a dog repeatedly when a violin is playing, after half a dozen or so times the dog will whimper and cower merely at the sound of the violin.27
There is no point in denying that Descartes' vivisection and ill-treatment of animals is disgraceful. If this smacks of hindsight, courtesy of our more sensitive and sentimental contemporary attitudes to animals, then so be it. It is hard to understand how any intelligent person could fail to recognise the vivid presence of emotion and sensation in animals, especially the dogs and horses they had most dealings with, or to ask themselves what the point would be for animals to display exact behavioural analogues of human pain and emotion if they lacked the conscious qualia of these things within. Famously, the "argument from analogy" which says that we can infer the presence of conscious experience in another creature (human or animal) when its outward behaviour resembles our own when we have just such conscious experience, is vulnerable to sceptical challenge; for an actor can seem to bleed and weep while feeling no pain, and there are creatures which suffer from a condition that makes them wholly insensate, despite being outwardly normal.28 But the supposition that all creatures other than oneself lack conscious experience, emotion and sensation, despite the intimate similarity of anatomy, environment and behaviour, is irrational; and it was frankly irrational of Descartes and his contemporaries to think in these terms about animals.
Of course, their real reason for doing so was theological; the thought that dogs and horses might have souls (and might accordingly go to heaven, or a canine or equestrian version of heaven), seemed to them preposterous, given that they had accepted the equally remarkable premise that there are such things as souls in the first place. And what use is a soul in a body unless to give it reason and experience, emotion and feeling? It follows that in lacking souls, dogs and other animals lack all that appertains to souls—and so could be cut open and experimented upon with impunity. One legend has it that, while living in Leiden, Descartes threw a cat out of a first floor window to demonstrate its lack of emotion and sensation (how defenestration was supposed to establish this is unclear), and I have seen the window in question, for it is still pointed out by the managers of an hotel located directly opposite the house, from which it is separated by a canal.
If nothing else, these aspects of Descartes' thought establish his bona fides on the theological front. The fact that he inserted his finger into the heart of a dying dog, having first sliced off the heart's apex, shows that he really held the standard view, or something very like it, about souls and their exclusivity to human beings.
Descartes' work on Le Monde was nothing if not up to date. In 1629 and again in 1630 a Jesuit astronomer called (rather appropriately) Christopher Scheiner had observed at Rome the phenomenon of parhelia—this being the appearance of "sundogs" or mock suns beside the real sun, caused by refraction of sunlight through ice crystals in the earth's atmosphere when the sun is near the horizon. Descartes wrote to Mersenne to get full details of Scheiner's account, and to ask for the latest observations and theories on comets. "For the last two or three months I have been quite caught up in the heavens. I have discovered their nature and the nature of the stars we see there and many other things which a few years ago I would not even have dared to hope to discover," he wrote, displaying nothing if not magnificent confidence in his work.29
All through 1632 and into the summer of 1633 Descartes worked apace at Le Monde, much of the time at Henry Reneri's home in Deventer, writing often to Mersenne for information and to keep him up to date with progress. In July 1633 he told Mersenne that the book was nearly finished, and promised to send him a copy of the manuscript before the end of the year. Galileo's Dialogue Concerning the Two Chief World Systems had been published just recently, in 1632, and Descartes asked Mersenne to tell him what Galileo had to say about such matters as the speed of falling bodies and the ebb and flow of tides. As this shows, Descartes had not been able to get hold of a copy of Galileo's book, which nevertheless was making a stir in scientific circles.
And not only in scientific circles; for the book had stirred theological circles also, and to no good end. In the summer of 1633 Galileo was arrested and condemned by the Inquisition, and all copies of his Dialogue Concerning the Two Chief World Systems available in Rome were burned. This was a terrible shock to Descartes. He immediately abandoned his plans to publish Le Monde, and wrote in trepidation to Mersenne:
I had intended to send you my World as a New Year gift, and only two weeks ago I was quite determined to send you at least part of it, if the whole work could not be copied in time. But I have to say that in the meantime I took the trouble to enquire in Leiden and Amsterdam whether Galileo's World System was available, for I thought I had heard that it was published in Italy last year. I was told that it had indeed been published but that all the copies had immediately been burned at Rome, and that Galileo had been convicted and fined. I was so astonished at this that I almost decided to burn all my papers or at least to let no one see them. For I could not imagine that he—an Italian, and as I understand in the good graces of the Pope—could have been made a criminal for any other reason than that he tried, as he no doubt did, to establish that the earth moves. I know that some Cardinals had already censured this view, but I thought I had heard it said that all the same it was being taught publicly even in Rome. I must admit that if the view is false, so too are the entire foundations of my philosophy, for it can be demonstrated from them quite clearly. And it is so closely interwoven in every part of my treatise that I could not remove it without rendering the whole work defective. But for all the world I did not want to publish a discourse in which a single word could be found that the Church would have disapproved of; so I preferred to suppress it rather than to publish it in a mutilated form.30
Under the impact of the shock about Galileo, and presumably for public consumption, given that much of the content of his letters to Mersenne was communicated to others—Mersenne being such a tireless epistolary clearing-house for communication among savants—Descartes' remarks about asiduously avoiding theological offence were evidently intended as an insurance policy, in case he somehow got into trouble. In this pusillanimous and frankly unconvincing vein, given his obvious ambition, he continued: "I have never had the inclination to produce books, and would never have completed it if I had not been bound by a promise to you and some other of my friends; it was my desire to keep my word to you that constrained me all the more to work at it. But after all I am sure you will not send a bailiff to force me to discharge my debt, and you will perhaps be quite glad to be relieved of the trouble of reading wicked doctrines. There are already so many views on philosophy which are merely plausible and which can be maintained in debate, that if my views are no more certain and cannot be approved of without controversy, I have no desire ever to publish them."31
But after all these protestation
s, the manuscript that Descartes was going to burn, then keep secret, and which he hoped would not offend the Church, and which might contain wicked doctrines, and which he never wanted to write—this manuscript would after all be sent to Mersenne: "Yet, after having promised you the whole work for so long," he disingenuously continued, "it would be bad faith on my part if I tried to satisfy you with trifling pieces; so as soon as I can I shall let you see what I have composed after all, but I ask you to be so kind as to allow me a year's grace so that I can revise and polish it. You drew my attention to Horace's saying, 'Keep back your work for nine years,' and it is only three years since I began the treatise which I intend to send to you." And then, suddenly anxious again, he added, "I ask you also to tell me what you know about the Galileo affair."32
The Galileo affair is a significant one, not only for the story of Galileo himself but because it marks the last major throw of the dice for the Church in its Canute-like effort to stop the tide of science. What was at issue was the Copernican model in which the earth goes round the sun, and its direct conflict with scripture. In the beautiful words of the King James version of Psalm 104, the text cited by the Church states:
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