Front Page Titles (by Subject) VI.: The Criterion of Truth . - The Method, Meditations and Philosophy of Descartes
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VI.: The Criterion of Truth . - Réné Descartes, The Method, Meditations and Philosophy of Descartes 
The Method, Meditations and Philosophy of Descartes, translated from the Original Texts, with a new introductory Essay, Historical and Critical by John Veitch and a Special Introduction by Frank Sewall (Washington: M. Walter Dunne, 1901).
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Descartes sought to evolve a criterion of truth from the first indubitable position. This was the clearness and distinctness of knowledge. He has defined this test in the following words: “I call that clear which is present and manifest to the mind giving attention to it, just as we are said clearly to see objects when, being present to the eye looking on, they stimulate it with sufficient force, and it is disposed to regard them; but the distinct is that which is so precise and different from all other objects as to comprehend in itself only what is clear.”
This test is evidently derived from reflection on intuitional knowledge. It is involved in his first truth, but it is not the sole guarantee of that truth; for this, as we have seen, is ultimately non-contradiction. His first truth could hardly be taken as affording the strict conditions of all truth, for in this case truth would need to be both direct and necessary. Certain principles might be so, but even in respect of them, it would exclude the idea of derivation and subordination, and lead to the idea of independent reality and guarantee. And the test would exclude all derivative knowledge, even when it was hypothetically necessary. Further, if it were set up as the absolute standard of truth, contingent or probable truth would be altogether excluded from the name. Descartes thus contented himself with the general statement of clearness and distinctness; and his first truth is accepted in its fullness as simply the basis of deduction — as the ground whence he may proceed to build up a philosophy of God and the material non-Ego.
The criterion is, however, ambiguous in its applications. When it is said that whatever we clearly and distinctly conceive is true, we may mean that it is possible — i. e., an ideal possibility; or we may mean that it is real — i. e., a matter of fact or existence. And Descartes has not always carefully distinguished those senses of the word true — as, for example, in his proof of the being of Deity from the notion. If we take the formula in the latter sense, we are led to identify truth with notional reality and its relations — thought with being.
The best criticism of the Cartesian criterion is unquestionably that given by Leibnitz in his famous paper— “Meditationes de Cognitione, Veritate, et Ideis.” He indicates with singular felicity the various grades of our conceptual knowledge. Cognition is obscure, when the object is not distinguished from other objects or the objects around it. Here the object is a mere something—not nothing; but what it precisely is, either in its own class of things or as contrasted with other things, we do not apprehend. Cognition, again, is clear, when we are able definitely to comprehend the object as in contradistinction from others. Clear cognition is further divided into Confused and Distinct. It is confused when we are unable to enumerate the marks or characters by which the object is discriminated from other objects, while it yet possesses such marks. Thus we can distinguish colors, odors, tastes, from each other; yet we cannot specify the marks by which we do so. At the same time such marks must exist, seeing the objects are resolvable into their respective causes. Our knowledge, again, is distinct when we can specify the discriminating marks, as the assayers in dealing with gold; and as we can do in the case of number, magnitude, figure. But distinct knowledge may still further be Inadequate or Adequate. It is inadequate when the discriminating marks are not analyzed or resolved into more elementary notions, being sometimes clearly and sometimes confusedly thought — as for example, the weight and color of gold. Knowledge, again, is adequate when the marks in our distinct cognition are themselves distinctly thought — that is, carried back by analysis to an end or termination. Whether any perfect example of this exists is, in the view of Leibnitz, doubtful. Number is the nearest approach to it. Then there is the distinction of the Blind or Symbolical and the Intuitive in cognition — the former being the potentiality of conception which lies in terms; the latter being the clear and distinct or individual picture of each mark so lying undeveloped. When cognition is at once adequate and intuitive, it is Perfect. But Leibnitz here at least hesitates to say whether such can be realized. To distinct cognition there attaches Nominal Definition. This is simply the evolution of the distinct knowledge, the drawing out of the marks which enable us to distinguish an object from other objects. But deeper than this lies Real Definition. This makes it manifest that the thing conceived or alleged to be conceived is possible. This test of the possible is the absence of contradiction in the object thought; the proof of the impossible is its presence. Possibility is either a priori or a posteriori—the former, when we resolve a notion into other notions of known possibility; the latter, when we have experience of the actual existence of the object; for what actually exists is possible. Adequate knowledge involves cognition through means of a priori possibility. It involves analysis carried through to its end. But Leibnitz hesitates to say that adequate cognition is within our reach. “Whether such a perfect analysis of notions can ever be accomplished by man — whether he can lead back his thoughts to first possibles (prima possibilia) and irresolvable notions, or, what comes to the same thing, to the absolute attributes of God themselves, viz, the first causes,— I do not now dare to determine.”
Leibnitz properly applies his distinction of nominal and real definition to the Cartesian proof of the reality of Deity from the notion of the most perfect being. This he says is defective as a proof in the hands of Descartes. It would be correct to say that God necessarily exists, if only he is first of all posited as possible. So long as this is not done, the argument for his existence does not amount to more than a presumption. But Descartes has either relied on a fallacious proof of the possibility of the divine existence, or he has endeavored to evade the necessity of proving it. That this proof can be supplied Leibnitz believes, and with this preliminary requisite fulfilled, he accepts the Cartesian argument.
It is obvious that the proper position of the criterion of Leibnitz as given in the real definition is at the very beginning of a system of knowledge. Possibility, or the absence of contradiction, underlies, in fact, clearness and distinctness. It is essential to the unity of any object of thought. The furthest point in abstraction to which we can go back is some being or some object, — something as opposed to nothing or non-being. But even this something must be at least definitely thought or distinguished from its contradictory opposite non-being or nothing. If it were not, the knowledge would be impossible. Its reality as a positive notion depends on this. Nay, even the negation, non-being or nothing, depends for any meaning it possesses on the positive being an object of knowledge The correlation here is not between two definite elements; one known as positive, the other as negative; there is correlation, but there is no correality. The negative side is satisfied by mere negation, as in the parallel case of one and none. And no reconciling medium is conceivable—none is possible to thought. If so, let it be named. To galvanize the negative into a positive in such a case, and call it synthetic thought, is simply to baptize the absurd. This solid advance on Descartes is virtually due to the acute and accurate mind of Leibnitz. It is our main safeguard against fantastic speculation.
The most liberal, and probably the fairest interpretation of the criterion of Descartes is, that it is the assertion of the need of evidence, whatever be its kind, as the ground of the acceptance of a statement or proposition. As such, it is the expression of the spirit of the philosophy of Descartes, and of the spirit also of modern research. As evidence must make its appeal to the individual mind, it may be supposed that this principle leads to individualism in opinion. This is certainly a possible result, but it is not essential to the principle. Evidence may be, nay, is at once individual and universal. The individual consciousness may realize for itself what is common to all; and indeed has not reached ultimate evidence until it has done so. And, however important may be the place of history, language, and social institutions in the way of a true and complete knowledge of mind or man, even these must appeal in the last resort to the conscious laws and processes of evidence, as embodied in the individual mind.
From his virtually making truth lie in a definite and high degree of conscious activity, Descartes was naturally led to regard error as more or less a negation, or rather privation. This idea he connects with Deity. Error is a mere negation, in respect of the Divine action; it is a privation in respect of my own action, inasmuch as I deprive myself by it of something which I ought to have and might have.
He thus develops his doctrine of Error.
Error is thus no direct consequence of finitude; only the possibility of it is so. It is properly to be regarded as the result of privation, and this is my own wilful act. It should, however, be observed here, that Descartes's positions regarding the will do not appear to be consistent. The two definitions of liberty which he gives are exclusive of each other. We cannot be conceived absolutely free in respect of two given alternatives, and yet free when the inclination of the will follows the greater clearness of the Understanding. The former is the liberty of indifference; the latter is simply that of spontaneity,— the spontaneity being relative to a previous or conditioning state of the consciousness.
It is further clear from the statements now quoted, that Descartes did not regard the Ego of consciousness as either a negation, non-entity, or illusion, as is represented, but a very definite and real positive — a mean, as he puts it, between absolute existence on the one side, and non-existence on the other. He certainly did not hold that the finite consciousness, so far as finite is either an error or an illusion. On the contrary, it is with him the basis of the very possibility of knowledge, and the type and warrant of a higher consciousness. And what other ground is possible? If the finite by itself be regarded as an illusion, and the infinite by itself be regarded as the same, it is curious to find that the two together make up reality. In this case, the relation between infinite and finite may be assumed as the true reality. So long as we hold the relation in consciousness, infinite and finite are known, and therefore real. But ere we can make this out, we must vindicate the possibility of a conscious relation between two terms, in themselves incognizable, non-existent, or illusory. Being must thus mean a groundless relation suspended in vacuo.
Nor is there anything special to his doctrine of Error which logically compels him to hold those conclusions. Principles of inference entirely foreign to his system and habit of thought may be assumed, and conclusions of this sort thus forced on his premises. It may, for example, be said, with Spinoza, that “determination is negation,” and that the finite, as finite, is a mere negation or nonentity; because it is a negation of the absolute substance, or of an Infinite Ego, or Infinite Self-consciousness — whatever ambiguity such phrases may be supposed to cover. But this may be said of any doctrine whatever which recognizes the Ego of consciousness as simply a fact or reality. And the principle of every determination being a negation is neither unambiguous nor self-evident; in several senses, it is rather self-condemned. It stands in need, at least, of thorough and precise vindication ere it is of use in any process of inference. In this application, at any rate, it will be hard to show its consistency. We must have the proof, in the first instance, of the Absolute Substance or Infinite Ego which the being of the finite Ego negates. Is it said that the Infinite Ego is the necessary correlate of the finite Ego? What, then? Does this correlation imply that the correlate or Infinite Ego is real in the sense in which the Ego of consciousness is real? Or rather even, as it seems to be inferred, does it necessarily imply that the Ego of consciousness discovers itself not to be what it at first is conscious that it is, and is really only a mode of this truly existing Infinite Ego? These are points in the logic of the process which ought not to be passed over without notice or vindication. And even if we get somehow the length or the height of the so-called Infinite, we must then ask whether the Infinite Ego means merely the abstract notion of an Ego, or whether it means a self-conscious Ego that actually pervades all being. If the former, the so-called determination is but an instance of the contemporary realization of the individual fact and the general notion. If the latter, it is impossible that there can be a finite Ego at all. It is not possible even in correlation. But, secondly, the result is not either possible or consistent. If the definite Ego of consciousness loses hold of its determination or limitation, it loses hold of itself—it no longer is; if it retains its limit or determination, it is not the Infinite Ego; if it commits the absurdity of losing hold of it and yet retaining it, it loses bold of itself, but does not become the Infinite Ego; in plain words, the “I” of our consciousness cannot be both man and God. That the finite consciousness is the infinite or divine consciousness is asserted on such a principle; it is as far from proof as ever it was.