He lived in Holland for twenty years ( 1629-49), except for a few brief visits to France and one to England, all on business. It is impossible to exaggerate the importance of Holland in the seventeenth century, as the one country where there was freedom of speculation. Hobbes had to have his books printed there; Locke took refuge there during the five worst years of reaction in England before 1688; Bayle (of the Dictionary) found it necessary to live there; and Spinoza would hardly have been allowed to do his work in any other country.
I said that Descartes was a timid man, but perhaps it would be kinder to say that he wished to be left in peace so as to do his work undisturbed. He always courted ecclesiastics, especially Jesuits–not only while he was in their power, but after his emigration to Holland. His psychology is obscure, but I incline to think that he was a sincere Catholic, and wished to persuade the Church–in its own interests as well as in his–to be less hostile to modern science than it showed itself in the case of Galileo. There are those who think that his orthodoxy was merely politic, but though this is a possible view I do not think it the most probable.
Even in Holland he was subject to vexatious attacks, not by the Roman Church, but by Protestant bigots. It was said that his views led to atheism, and he would have been prosecuted but for the intervention of the French ambassador and the Prince of Orange. This attack having failed, another, less direct, was made a few years later by the authorities of the University of Leyden, which forbade all mention of him, whether favourable or unfavourable. Again the
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Prince of Orange intervened, and told the university not to be silly. This illustrates the gain to Protestant countries from the subordination of the Church to the State, and from the comparative weakness of Churches that were not international.
Unfortunately, through Chanut, the French ambassador at Stockholm, Descartes got into correspondence with Queen Christina of Swed.en, a passionate and learned lady who thought that, as a sovereign, she had a right to waste the time of great men. He sent her a treatise on love, a subject which until then he had somewhat neglected. He also sent her a work on the passions of the soul, which he had originally composed for Princess Elizabeth, daughter of the Elector Palatine. These writings led her to request his presence at her court; he at last agreed, and she sent a warship to fetch him ( September 1649). It turned out that she wanted daily lessons from him, but could not spare the time except at five in the morning. This unaccustomed early rising, in the cold of a Scandinavian winter, was not the best thing for a delicate man. Moreover Chanut became dangerously ill, and Descartes looked after him. The ambassador recovered, but Descartes fell ill and died in February 1650.
Descartes never married, but he had a natural daughter who died at the age of five; this was, he said, the greatest sorrow of his life. He always was well dressed, and wore a sword. He was not industrious; he worked short hours, and read little. When he went to Holland he took few books with him, but among them were the Bible and Thomas Aquinas. His work seems to have been done with great concentration during short periods; but perhaps, to keep up the appearance of a gentlemanly amateur, he may have pretended to work less than in fact he did, for otherwise his achievements seem scarcely credible.
Descartes was a philosopher, a mathematician, and a man of science. In philosophy and mathematics, his work was of supreme importance; in science, though creditable, it was not so good as that of some of his contemporaries.
His great contribution to geometry was the invention of co-ordinate geometry, though not quite in its final form. He used the analytic method, which supposes a problem solved, and examines the consequences of the supposition; and he applied algebra to geometry. In both of these he had had predecessors–as regards the former, even
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among the ancients. What was original in him was the use of coordinates, i.e., the determination of the position of a point in a plane by its distance from two fixed lines. He did not himself discover all the power of this method, but he did enough to make further progress easy. This was by no means his sole contribution to mathematics, but it was his most important.
The book in which he set forth most of his scientific theories was Principia Philosophiae, published in 1644. There were however some other books of importance: Essais philosophiques ( 1637) deals with optics as well as geometry, and one of his books is called De la formation du foetus. He welcomed Harvey’s discovery of the circulation of the blood, and was always hoping (though in vain) to make some discovery of importance in medicine. He regarded the bodies of men and animals as machines; animals he regarded as automata, governed entirely by the laws of
physics, and devoid of feeling or consciousness. Men are different: they have a soul, which resides in the pineal gland. There the soul comes in contact with the “vital spirits,” and through this contact there is interaction between soul and body. The total quantity of motion in the universe is constant, and therefore the soul cannot affect it; but it can alter the direction of motion of the animal spirits, and hence, indirectly, of other parts of the body.
This part of his theory was abandoned by his school–first by his Dutch disciple Geulincx, and later by Malebranche and Spinoza. The physicists discovered the conservation of momentum, according to which the total quantity of motion in the world in any given direction is constant. This showed that the sort of action of mind on matter that Descartes imagined is impossible. Assuming–as was very generally assumed in the Cartesian school–that all physical action is of the nature of impact, dynamical laws suffice to determine the motions of matter, and there is no room for any influence of mind. But this raises a difficulty. My arm moves when I will that it shall move, but my will is a mental phenomenon and the motion of my arm a physical phenomenon. Why then, if mind and matter cannot interact, does my body behave as if my mind controlled it? To this Geulincx invented an answer, known as the theory of the “two clocks.” Suppose you have two clocks which both keep perfect time: whenever one points to the hour, the other will strike, so that if you saw one and heard the other, you would think the one caused the other to strike. So it
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is with mind and body. Each is wound up by God to keep time with the other, so that, on occasion of my volition, purely physical laws cause my arm to move, although my will has not really acted on my body.
There were of course difficulties in this theory. In the first place, it was very odd; in the second place, since the physical series was rigidly determined by natural laws, the mental series, which ran parallel to it, must be equally deterministic. If the theory was valid, there should be a sort of possible dictionary, in which each cerebral occurrence would be translated into the corresponding mental occurrence. An ideal calculator could calculate the cerebral occurrence by the laws of dynamics, and infer the concomitant mental occurrence by means of the “dictionary.” Even without the “dictionary,” the calculator could infer any words and actions, since these are bodily movements. This view would be difficult to reconcile with Christian ethics and the punishment of sin.
These consequences, however, were not at once apparent. The theory appeared to have two merits. The first was that it made the soul, in a sense, wholly independent of the body, since it was never acted on by the body. The second was that it allowed the general principle: “one substance cannot act on another.” There were two substances, mind and matter, and they were so dissimilar that an interaction seemed inconceivable. Geulincx’s theory explained the appearance of interaction while denying its reality.
In mechanics, Descartes accepts the first law of motion, according to which a body left to itself will move with constant velocity in a straight line. But there is no action at a distance, as later in Newton’s theory of gravitation. There is no such thing as a vacuum, and there are no atoms; yet all interaction is of the nature of impact. If we knew enough, we should be able to reduce chemistry and biology to mechanics; the process by which a seed develops into an animal or a
