105. Thus the logic of Descartes, using that word for principles that guide our reasoning, was an instrument of defence both against the captiousness of ordinary scepticism, that of the Pyrrhonic school, and against the disputatious dogmatism of those who professed to serve under the banner of Aristotle. He who reposes on his own consciousness, or who recurs to first principles of intuitive knowledge, though he cannot be said to silence his adversary, should have the good sense to be silent himself, which puts equally an end to debate. But so far as we are concerned with the investigation of truth, the Cartesian appeal to our own consciousness, of which Stewart was very fond, just as it is in principle, may end in an assumption of our own prejudices as the standard of belief. Nothing can be truly self-evident, but that which a clear, an honest, and an experienced understanding in another man acknowledges to be so.
Treatise on art of logic. 106. Descartes has left a treatise highly valuable, but not very much known, on the art of logic, or rules for the conduct of the understanding.[254] Once only, in a letter, he has alluded to the name of Bacon.[255] There are perhaps a few passages in this short tract that remind us of the Novum Organum. But I do not know that the coincidence is such as to warrant a suspicion that he was indebted to it; we may reckon it rather a parallel, than a derivative logic; written in the same spirit of cautious, inductive procedure, less brilliant and original in its inventions, but of more general application than the Novum Organum, which is with some difficulty extended beyond the province of natural philosophy. Descartes is as averse as Bacon to syllogistic forms. “Truth,” he says, “often escapes from these fetters, in which those who employ them remain entangled. This is less frequently the case with those who make no use of logic, experience showing that the most subtle of sophisms cheat none but sophists themselves, not those who trust to their natural reason. And to convince ourselves how little this syllogistic art serves towards the discovery of truth, we may remark that the logicians can form no syllogism with a true conclusion, unless they are already acquainted with the truth that the syllogism develops. Hence it follows that the vulgar logic is wholly useless to him who would discover truth for himself, though it may assist in explaining to others the truth he already knows, and that it would be better to transfer it as a science from philosophy to rhetoric.”[256]
[254] M. Cousin has translated and republished two works of Descartes, which had only appeared in Opera Posthuma Cartesii, Amsterdam, 1701. Their authenticity, from external and intrinsic proofs, is out of question. One of these is that mentioned in the text; entitled “Rules for the Direction of the Understanding;” which, though logical in its subject, takes most of its illustrations from mathematics. The other is a dialogue, left imperfect, in which he sustains the metaphysical principles of his philosophy. Of these two little tracts, their editor has said, that “they equal in vigour and perhaps surpass in arrangement the Meditations and Discourse on Method. We see in these more unequivocally the main object of Descartes, and the spirit of the revolution which has created modern philosophy, and placed in the understanding itself the principle of all certainty, the point of departure for all legitimate inquiry. They might seem written but yesterday, and for the present age.” Vol. xi. preface, p. 1. I may add to this, that I consider the Rules for the direction of the Understanding as one of the best works on logic (in the enlarged sense) which I have ever read; more practically useful, perhaps, to young students than the Novum Organum; and though, as I have said, his illustrations are chiefly mathematical, most of his rules are applicable to the general discipline of the reasoning powers. It occupies little more than one hundred pages, and I think that I am doing a service in recommending it. Many of the rules will, of course, be found in later books; some possibly in earlier. This tract, as well as the dialogue which follows it, is incomplete, a portion being probably lost.
[255] Si quelqu’un de cette humeur vouloit entreprendre d’écrire l’histoire des apparences célestes selon la méthode de Verulamius. Vol. vi., p. 210.
[256] Vol. xi., p. 255.
Merits of his writings. 107. It would occupy too much space to point out the many profound and striking thoughts which this treatise on the conduct of the understanding, and indeed most of the writings of Descartes contain. “The greater part of the questions on which the learned dispute are but questions of words. These occur so frequently that, if philosophers would agree on the signification of their words, scarce any of their controversies would remain.” This has been continually said since; but it is a proof of some progress in wisdom, when the original thought of one age becomes the truism of the next. No one had been so much on his guard against the equivocation of words, or knew so well their relation to the operations of the mind. And it may be said, generally, though not without exception of the metaphysical writings of Descartes, that we find in them a perspicuity which springs from his unremitting attention to the logical process of inquiry, admitting no doubtful or ambiguous position, and never requiring from his reader a deference to any authority but that of demonstration. It is a great advantage in reading such writers that we are able to discern when they are manifestly in the wrong. The sophisms of Plato, of Aristotle, of the schoolmen, and of a great many recent metaphysicians, are disguised by their obscurity; and while they creep insidiously into the mind of the reader, are always denied and explained away by partial disciples.
His notions of free will. 108. Stewart has praised Descartes for having recourse to the evidence of consciousness in order to prove the liberty of the will. But he omits to tell us that the notions entertained by this philosopher were not such as have been generally thought compatible with free agency in the only sense that admits of controversy. It was an essential part of the theory of Descartes that God is the cause of all human actions. “Before God sent us into the world,” he says in a letter, “he knew exactly what all the inclinations of our will would be; it is he that has implanted them in us; it is he also that has disposed all other things, so that such or such objects should present themselves to us at such or such times, by means of which he has known that our free will would determine us to such or such actions, and he has willed that it should be so; but he has not willed to compel us thereto.”[257] “We could not demonstrate,” he says at another time, “that God exists, except by considering him as a being absolutely perfect; and he could not be absolutely perfect, if there could happen anything in the world which did not spring entirely from him.... Mere philosophy is enough to make us know that there cannot enter the least thought into the mind of man, but God must will and have willed from all eternity that it should enter there.”[258] This is in a letter to his highly intelligent friend, the princess Palatine Elizabeth, granddaughter of James I.; and he proceeds to declare himself strongly in favour of predestination, denying wholly any particular providence, to which she had alluded, as changing the decrees of God, and all efficacy of prayer, except as one link in the chain of his determinations. Descartes, therefore, whatever some of his disciples may have become, was far enough from an Arminian theology. “As to free will,” he says elsewhere, “I own that thinking only of ourselves we cannot but reckon it independent, but when we think of the infinite power of God we cannot but believe that all things depend on him, and that consequently our free will must do so too.... But since our knowledge of the existence of God should not hinder us from being assured of our free will, because we feel and are conscious of it in ourselves, so that if our free will should not make us doubt of the existence of God. For the independence which we experience and feel in ourselves, and which is sufficient to make our actions praiseworthy or blameable, is not incompatible with a dependence of another nature, according to which all things are subject to God.”[259]
[257] Vol. ix., p. 374.
[258] Id. p. 246.
[259] Vol. ix., p. 368. This had originally been stated in the Principia with less confidence, the free will of man and predetermination of God being both asserted as true, but their co-existence incomprehensible. Vol. iii., p. 86.