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DESCARTES 



that he had hitherto been taught, that it might be 

 free to receive the impressions of truth, whenceso- 

 ever they should come. In pursuance of his plan, 

 he resolved to travel, and soon entered the army as a 

 volunteer, serving successively in Holland, Bohemia, 

 and Hungary. It was while he was in winter-quar- 

 ters at Neuburg on the Danube ( St Martin's Eve, 

 1619, as he himself informs us) that there first 

 dawned upon him the principles of the new method 

 which he afterwards applied in philosophy and for 

 the reorganisation of knowledge generally. So in 

 1621 he left the army, but continued to travel as 

 a private gentleman, with occasional residences in 

 Paris, till 1629. In that year he retired to Holland, 

 where he lived in great seclusion for twenty years, 

 devoted to the elaboration of his discoveries and 

 the publication of his chief works. In time his 

 doctrines attracted many disciples in the land of his 

 adoption, but involved him at the same time in bitter 

 controversy with the Dutch theologians. These 

 unpleasant encounters had probably their share in 

 inducing him to accept an invitation to go to 

 Sweden, addressed to him by Queen Christina, who 

 desired his learned intercourse and instruction. 

 He left Holland in September 1648, but his consti- 

 tution was not able to stand the rigour of the 

 northern winter and the exposure involved in wait- 

 ing upon the queen at five every morning for an 

 hour's philosophical instruction. He died at Stock- 

 holm of inflammation of the lungs on February 11, 

 1650. Sixteen years later, his body was brought 

 to Paris, and buried in the church of St Genevieve- 

 du-Mont. In 1819 his remains were again trans- 

 ferred to St Germain-des-Pres, where they now 

 rest. 



The grand object towards which Descartes 

 directed his endeavours was the attainment of 

 philosophical certainty. The way whereby he 

 sought to attain this end is explained in the 

 Discourse on Method ( Discours de la Methode, pub- 

 lished in 1637 ). This small but extremely interest- 

 ing and important treatise contains a history of the 

 inner life or the author, tracing the progress of his 

 mental development from its commencement in 

 early years, to the point where it resulted in his 

 resolution to hold nothing for true until he had 

 ascertained the grounds of certitude. The author 

 also, in the same treatise, lays down the methodical 

 rules by which he resolved to guide his inquiries, 

 and by the observance of which he hoped to arrive 

 at absolute certainty, if indeed it were at all attain- 

 able. The results of his inquiries are indicated in 

 the Discourse, but are exhibited more particularly 

 in his Meditationes de Prima PhilosophiA (Amst. 

 1641 ), and the Principia Philosophice (Amst. 1644). 

 Doubt, according to Descartes, is the philosophic 

 starting-point, the solvent which we must bring to 

 bear upon all our inherited beliefs and opinions. 

 This doubt is to be distinguished from scepticism, 

 which is a permanent state of mind and involves 

 despair of truth. It is to be regarded simply as an 

 instrument of philosophical inquiry, and as such 

 has received the name of Cartesian doubt. Apply- 

 ing this test relentlessly to all that had hitherto 

 borne the name of knowledge, Descartes found one, 

 and only one proposition that seemed to him to 

 stand firm, and of which the truth could not possibly 

 be doubted : that proposition was that he existed, 

 which he inferred from the fact of his possessing 

 consciousness. He could not doubt that he felt and 

 thought, and therefore he could not doubt that he, 

 the feeler, the thinker, existed. This relation be- 

 tween consciousness and existence he expressed by 

 the memorable words : Cogito, ergo sum. On in- . 

 quiring further into the ground of his certitude in 

 the case of this proposition, Descartes was able to 

 assign no further reason than that he saw very 

 clearly that in order to think, it is necessary to exist. 



He formulated, therefore, the following criterion of 

 certainty that whatever is clearly and distinctly 

 thought, must be true. Amongst these clear and 

 distinct thoughts he soon recognised the idea of 

 God as the absolutely Perfect Being. This idea, he 

 reasoned, could not be formed in our minds by our- 

 selves, for the imperfect can never originate the 

 perfect ; it must be connate i.e. part of the original 

 structure of our understanding, and implanted there 

 by the Perfect Being himself. Hence, from the 

 existence of the idea of perfection, Descartes inferred 

 the existence of God as the originator of it ; he in- 

 ferred it also from the mere nature of the idea, 

 because the idea of perfection involves existence. 

 The latter is known as the ontological argument, 

 which Descartes thus reintroduced into modern 

 philosophy. But if God exist, then we have a guar- 

 antee, according to Descartes, of the previously 

 determined ground of certitude, for God the Per- 

 fect Being cannot deceive, and therefore what- 

 ever our consciousness clearly testifies may be 

 implicitly believed. 



The most general fundamental principle of the 

 philosophical system of Descartes is the essential 

 difference or dualism of spirit and matter the 

 thinking and the extended substances a difference 

 so great, according to Descartes, that they can 

 exert no influence upon each other. Mind or spirit 

 is pure consciousness, and matter is mere extension ; 

 these attributes are mutually exclusive, and hence 

 these two ' created substances ' can be united (as we 

 find them, for example, in the human being) only 

 through tlie intervention of the infinite substance 

 or God. This doctrine led directly to the system 

 called occasionalism, the principle of which was 

 that body and mind do not really affect eacli 

 other, God being always the true cause of the 

 apparent influence of one on the other. A volition 

 on our part is merely the occasion of God's produc- 

 ing a corresponding bodily motion, and similarly 

 the material processes in the nerves and brain are 

 only the occasion, not the cause, of the ensuing 

 mental result. This doctrine was further developed 

 by Leibnitz in connection with his doctrine of pre- 

 established harmony (see LEIBNITZ). The human 

 body being thus a mere machine accidentally united 

 to a rational soul, it was an immediate consequence 

 of the Cartesian doctrine that animals (in which 

 the rational soul is absent) are literally automata ; 

 their cries no more imply feeling than the creaking 

 of a machine. This ruthless product of logical con- 

 sistency unfortunately led to cruelty in practice. 



Descartes did not confine his attention to mental 

 philosophy. His philosophy is in fact only the 

 introduction to an elaborate system of physics. In 

 this department it is noteworthy that he completely 

 discarded final causes and proposed to himself the 

 explanation of all physical phenomena from matter 

 and motion. His celebrated theory of vortices, de- 

 vised to explain the motions of the heavenly bodies, 

 held the field till it was superseded, after a stubborn 

 resistance, by the Newtonian theory of gravitation. 

 It was in mathematics, however, that Descartes 

 achieved the greatest and most lasting results. It 

 was Descartes who first recognised the true meaning 

 of the negative roots of equations ; arid we owe to 

 him the theorem, which is called by his name, that 

 an equation may have as many positive roots as 

 there are changes of sign in passing from term to 

 term, and as many negative roots as there are con- 

 tinuations of sign, and not more of either kind. He 

 gave a new and ingenious solution of equations of 

 the fourth degree ; and first introduced exponents, 

 and thereby laid the foundation for calculating with 

 powers. He showed, moreover, how to draw tan- 

 gents and normals at every point of a geometrical 

 curve, with the exception of mechanical or trans- 

 cendental curves ; and what perhaps was his highest 



