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Descartes affirms that the precondition to the attainment of truth is thorough-going doubt. Not doubt merely for its own sake, however; scepticism is only a means to an end, a moment or element of method, not the goal of thought. And it must be remembered, of course, that the principle of universal doubt has application in theoretical matters only; in matters pertaining to conduct, says Descartes, we must follow as principle that which is merely probable. Now it is, in the first instance, easy to doubt all forms of so-called knowledge, except mathematics. Mathematics, therefore, suggests, if it does not immediately contain, the ideal of scientific method; it is not merely formal, like the old logic, — not merely the rule of the operation of a certain subjective faculty, but is a method of arriving at objective truth of fact; and it possesses the highest degree of certainty. But the method sought must be absolutely universal, which mathematics is not. It has four elementary principles, which in their relation to one another are but steps in a single process, whose unity corresponds to the nature of truth itself. These principles or steps are as follows: (1) Never receive as true anything not certainly known to be such; avoid prejudice and precipitancy in judgment, and embrace nothing except that which presents itself so clearly and distinctly to the mind that there is no room for doubt about it; (2) Analyze every problem into as many parts as possible and as may best facilitate its solution; (3) Think in an orderly manner, commencing with objects that are the simplest and easiest to understand, and ascending by degrees to the knowledge of the most complex, assuming the same order among those which do not naturally have the precedence one over the other; (4) Make everywhere enumerations so complete and reviews so comprehensive as to be assured of having omitted nothing. Descartes, it is true, gives this as merely the method which he had resolved upon to assure himself personally of rising out of the region of confused, obscure, and, hence, doubtful things into that of clear and distinct truth; but he asserts,

nevertheless, that diversity of opinion results not so much. from differences in minds as in methods of using them; that truth is the same for all minds following the true method; and, furthermore, the method of analysis and synthesis embodied in his four principles is, as we shall see, quite in harmony with the physico-mechanical character of his doctrines.1

Metaphysics: The First Principle, "Cogito, ergo sum." -If the truth is that only which is absolutely certain, which is perfectly clear and distinct to the mind, it would appear, at first, at least, that nothing whatever can be received as true. The presentations of the senses, of memory, of imagination, may all easily be questioned, may be treated as dreams, mere hallucinations, the machinations, say, of some omnipotent deceiver: they are, if believed in, mere prejudices and presuppositions, which have to be got rid of. But there is one prejudice that I cannot rid myself of: I think, and (therefore) I am. However questionable all my ideas considered as representations of fact, it is not at all questionable that I have them: I could not be deceived if I did not have them, did not think (in the broad sense of the term), and hence did not exist. If it be said that I reply that I cannot

am deceived in thinking that I exist, I here make a distinction between my existing and my thinking that I exist. I can not with such certainty say, “I walk, therefore I exist," because it is not absolutely certain to the understanding-however it may be to sense-that I do walk. My existence and my thinking are to understanding inseparable; walking and my existence are not thus inseparable. The reasoning of Cogito, ergo sum, is not purely syllogistic. There is not wanting a premise to complete my thought, as the premise, Whatever thinks exists. I immediately perceive intellectually my existence as a thinking being. Further, I perceive that I exist as thinking. I do not as yet perceive anything beyond that; my doubt and 2 First Meditation.

1 Discours de la Méthode.

3 Second Meditation.

4 Ibid.

4

those creations of my imagination, the truth of which I can easily doubt, prove only that I exist as thinking. This principle, Cogito, ergo sum, is, then, the first material principle of philosophy; it is the foundation and criterion of all truth, and may fitly be compared to the single fixed point Archimedes required (but could not get) to move the whole world with his lever. In the intellectual perception of myself I have that feeling of certainty and that clearness and distinctness of idea which gives to mathematical truth its almost supreme value as regards method. All other ideas are true in so far as they possess the clearness and distinctness of this. In fine, whatever assertion I make concerning the existence of other beings than myself involves, as its support, the assertion of my own existence, and is to be judged by comparison with my assertion as to my own existence.1

The Knowledge of other Existences than Self: (1) God.

Now with regard to the existence of other beings than myself there is a possibility of my being deceived. To resolve the doubt here I am obliged to determine whether or not there be a God, and, if there is, whether or not he can be a deceiver. Where do I get the idea of a God, and what truth is there in it? Of all my ideas, I find some that have come from without, as those of sensible existences, others that are created purely by myself, such as those of a winged horse or a siren, and others still that neither come from without nor are created by myself, and must therefore be, as it were, innate; for example, the idea of truth, thing, thought, an infinite being. That the idea of an infinite being does not come to me from without, is self-evident; that it has not been produced by me may be argued from the fact that an effect can in no case be greater than its cause; e.g., the perfect cannot in any way be an effect of the imperfect. I can easily produce, by abstraction, the idea of the indefinite; but not the positive idea of infinite perfection, for I am imperfect. The source of such an idea

1 See Second Meditation.

can, originally, be only a being that is infinite in nature, i. e., God; therefore the idea must have been implanted in me by him, he must exist. I know that God exists also from the fact of my own existence; if I had been the author of my own being, I should have given myself all possible perfection, and I must attribute my continued existence as well as my creation to a God.1 Further, the existence of God may and must be inferred from the very idea of the infinite. It is as impossible for me to conceive the idea of infinite perfection without that of existence as it is to conceive a triangle the sum of whose angles is not two right angles, or to conceive a mountain without a corresponding valley. I have, in other words, a distinct and clear perception of existence as a necessary attribute of an infinitely perfect nature. I can, it is true, separate in thought the idea of a finite thing and the existence of that finite thing; but the idea of the infinite would be self-contradictory and impossible to me if it did not include that of God's existence. This proof of the existence of God, which resembles that of Anselm, is distinguished from the Anselmic proof as follows: Anselm infers the existence of God purely from the necessary implication of the idea of the perfect being; I rather from the clearness and distinction with which the necessary connection between infinitude and existence is perceived by the understanding.

Existence of the External World. Now, it is utterly impossible that God, a being of infinite perfection, can wish to deceive me. I know, therefore, that whatever I can clearly and distinctly conceive as existing does really exist, just as I know that God exists from the clear and distinct conception of him. I clearly and distinctly conceive the external world as existing, (ergo) it really exists.

Substances. Among my ideas are ideas of things that are clearly and distinctly conceivable in and by themselves, and ideas of others that are not so conceivable. I can, 2 Fifth Meditation.

1 Third Meditation.

3 Fifth Meditation.

There are

for example, clearly and distinctly conceive myself as a purely intellective being, as complete without the faculties of feeling and imagination; but I cannot conceive imagination and feeling as existent without me or some intelligent nature to which they belong; nor can I conceive the power of changing place and taking various situations without a certain nature to which it belongs. Things which are thus conceivable in themselves are substances; things not thus conceivable are attributes or are modes. three substances: God, ourselves, and external nature. Ourselves we know as thinking substance, God we know also as thinking substance and as author of ourselves and external nature, and nature we know, from the veracity of God, as extended substance. Primarily, God alone is substance, since we and nature depend on him; we and nature are secondary substances, having the attributes respectively of thought and extension.

Nature. According to his view of substance, Descartes. could not conceive nature as really distinct from God; nor did he, except for purposes of mere explanation. And for purposes of explanation he finds it necessary, in accordance with his mathematical method of knowledge, to treat of nature as mere extension and motion. The conception of force or power he expressly terms non-physical, power belongs to God alone; and he excludes all interpretation of nature by the doctrine of final causes. Absolutely considered, nature is to Descartes eternal; and yet he finds it necessary for explanation's sake, and convenient for theology's sake, to treat nature as having a certain origin from material elements and motion. Extension is without limitation of any nature; hence there are no fixed atoms and no vacuum. Original matter (extension) is divided into innumerable undifferentiated parts set and kept in motion by the power of God. From the collision of the parts of moving matter there results a differentiation of matter into three sorts: (1) "first matter," comprising innumerable fine particles, materia subtilissima,

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