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hardly impair, Descartes possessed, in addition, a rare mastery of the art of literary expression. If the "Discours de la Méthode" had no other merits, it would be worth study for the sake of the luminous simplicity and sincerity of its style.
A mathematician of the very first rank, Descartes knew all that was to be known of mechanical and optical science in his day; he was a skilled and zealous practical anatomist; he was one of the first to recognise the prodigious importance of the discovery of his contemporary Harvey; and he penetrated more deeply into the physiology of the nervous system than any specialist in that science, for a century, or more, after his time. To this encyclopædic and yet first-hand acquaintance with the nature of things, he added an acquaintance with the nature of men (which is a much more valuable chapter of experience to philosophers than is commonly imagined), gathered in the opening campaigns of the Thirty Years' War, in wide travels, and amidst that brilliant French society in which Pascal was his worthy peer. Even a "Traité des Passions," to be worth anything, must be based upon observation and experiment; and, in this subject, facilities for laboratory practice of the most varied and extensive character were offered by the Paris of Mazarin and the Duchesses; the Paris, in which Descartes' great friend and ally, Father Mersenne, reckoned atheists by the thousand; and, in which,
political life touched the lowest depths of degradation, amidst the chaotic personal intrigues of the Fronde. Thus endowed, thus nurtured, thus tempered in the fires of experience, it is intelligible enough that a resolute, clear-headed man, haunted from his youth up, as he tells us, with an extreme desire to learn how to distinguish truth from falsehood, in order to see his way clearly and walk surely through life,1 should have early come to the conclusion, that the first thing to be done was to cast aside, at any rate temporarily, the crutches of traditional, or other, authority; and stand upright on his own feet, trusting to no support but that of the solid ground of fact.
It was in 1619, while meditating in solitary winter quarters, that Descartes (being about the same age as Hume when he wrote the "Treatise on Human Nature") made that famous resolution, to "take nothing for truth without clear knowledge that it is such," the great practical effect of which is the sanctification of doubt; the recognition that the profession of belief in propositions, of the truth of which there is no sufficient evidence, is immoral; the discrowning of authority as such; the repudiation of the confusion, beloved of sophists of all sorts, between free assent and mere piously gagged dissent; and the admission of the obligation to reconsider even one's axioms on due demand.
These, if I mistake not, are the notes of the 1 Discours de la Méthode. 1. Partie.
modern, as contrasted with the ancient spirit. It is true that the isolated greatness of Socrates was founded on intellectual and moral characteristics of the same order. He also persisted in demanding that no man should "take anything for truth without a clear knowledge that it is such," and so constantly and systematically shocked authority and shook traditional security, that the fact of his being allowed to live for seventy years, if one comes to think of it, is evidence of the patient and tolerant disposition of his Athenian compatriots, which should obliterate the memory of the final hemlock. That which it may be well for us not to forget is, that the first-recorded judicial murder of a scientific thinker was compassed and effected, not by a despot, nor by priests, but was brought about by eloquent demagogues, to whom, of all men, thorough searchings of the intellect are most dangerous and therefore most hateful.
The first agnostic, the man who, so far as the records of history go, was the first to see that clear knowledge of what one does not know is just as important as knowing what one does know, had no true disciples; and the greatest of those who listened to him, if he preserved the fame of his master for all time, did his best to counteract the impulse towards intellectual clearness which Socrates gave. The Platonic philosophy is probably the grandest example of the unscientific use of the imagination extant; and it
would be hard to estimate the amount of detriment to clear thinking effected, directly and indirectly, by the theory of ideas, on the one hand, and by the unfortunate doctrine of the baseness of matter, on the other.
Ancient thought, so far as it is positive, fails on account of its neglect to criticise its assumptions; so far as it is negative, it fails, because it forgets that proof of the inconsistencies of the terms in which we symbolise things has nothing to do with the cogency of the logic of facts. The negations of Pyrrhonism are as shallow, as the assumptions of Platonism are empty. Modern thought has by no means escaped from perversions of the same order. But, thanks to the sharp discipline of physical science, it is more and more freeing itself from them. In face of the incessant verification of deductive reasoning by experiment, Pyrrhonism has become ridiculous; in face of the ignominious fate which always befalls those who attempt to get at the secrets of nature, or the rules of conduct, by the high a priori road, Platonism and its modern progeny show themselves to be, at best, splendid follies.
The development of exact natural knowledge in all its vast range, from physics to history and criticism, is the consequence of the working out, in this province, of the resolution to "take nothing for truth without clear knowledge that it is such; to consider all beliefs open to criticism; to regard
the value of authority as neither greater nor less, than as much as it can prove itself to be worth. The modern spirit is not the spirit "which always denies," delighting only in destruction; still less is it that which builds castles in the air rather than not construct; it is that spirit which works and will work "without haste and without rest," gathering harvest after harvest of truth into its barns and devouring error with unquenchable fire.
In the reform of philosophy, since Descartes, I think that the greatest and the most fruitful results of the activity of the modern spirit-it may be, the only great and lasting results-are those first presented in the works of Berkeley and of Hume.
The one carried out to its logical result the Cartesian principle, that absolute certainty attaches only to the knowledge of facts of consciousness; the other, extended the Cartesian criticism to the whole range of propositions commonly "taken for truth;" proved that, in a multitude of important instances, so far from possessing "clear knowledge" that they may be so taken, we have none at all; and that our duty therefore is to remain silent; or to express, at most, suspended judgment.
My earliest lesson on this topic was received from Hume's keen-witted countryman Hamilton;