Platonic Theory of Ideas

Satisfied that the heterogeneous and disconnected principles on which the science of the time proceeded in no sense fulfilled these requirements, Descartes resolved to doubt provisionally all the beliefs and opinions with which he had grown up, until by a process of elimination he should reach at last a datum so clear and distinct that doubt with respect to it was no longer possible. Neither in the realm of sense-perception nor even in the realm of mathematical science could such a datum be found, for sense experience is often illusory and we can never be sure that it is not, and so far as their relation to the mind is concerned mathe matical principles may be deceptive. Ultimately, then, he was left with the bare fact of thinking or being conscious. Cogito ergo sum; the thinker could not doubt the fact of his own con sciousness, for that was as necessarily manifest in his doubting as in his knowing. He exists through being conscious; and his being conscious assures him with indubitable certainty that he is at least part of the realm of existence. In the fact of self-conscious ness, Descartes wants to say, truth and existence are identical.

Conscious Existence.

The dictum was serviceable mainly as affording a clue to a quite general rule or criterion of certitude: whatsoever is apprehended with the same degree of clearness and distinctness as the connectedness of consciousness and existence in the proposition cogito ergo sum is true. Or conversely, where we can disjoin our ideas, and clearly and distinctly apprehend them as separate, there we are bound to deny that the existents we take to correspond to them are necessarily conjoined or im plied in one another. A rapid application of this rule led Descartes at once to certain fundamental positions in regard to the facts of experience. The notion of conscious existence does not imply that of extended body; and in like manner the notion of extended body does not imply that of consciousness. Mind and body are, therefore, not necessarily connected, but must be regarded as independent of one another; and if they be in any way con joined, the conjunction must be contingent.

So, too, we can distinguish between the essential and the acci dental attributes of each of these types of existents. Extended ness is obviously the essential attribute of the corporeal, but in the notion of extendedness there is not involved that of move ment. Movement in the external world must, therefore, be re garded as a contingent addition. Similarly, in the inner world, Descartes was inclined to regard the understanding (intellectus) as the essential attribute, and the will (voluntas) as a contingent one. It is noteworthy that the opposition expressed by the terms extendedness and movement comes very near to the opposition in the Platonic system. So far as the essence of the corporeal world is concerned, we might work out a complete geometrical explanation. Our propositions would, in that case,

be all universal in significance; they would define the character of any change, if change occurred, but they would not determine the conditions under which any change might, or must, occur. Moreover, in regard to any actual change taking place in time, it is impossible to maintain that in the notion of what precedes there is implied the notion of what succeeds. For each content of each moment of time can be conceived separately. There is nothing in the fact that the real world has been so far kept in ex istence which renders it necessary that it should go on existing.

Epistemologically considered, then, the Cartesian doctrine of nature brings into prominence the opposition between two types of propositions. On the one hand, there are propositions which constrain assent so soon as their terms are understood, which are seen to be absolutely necessary; truths of reason, as we may call them. On the other hand, there are propositions the truth of which, if they can be said to be true, must be described as con tingent ; their validity is not guaranteed by the relation in which the ideas contained in them stand to one another. They may be called truths of fact.

It is in reference to the latter class of truths that the crucial difficulties of the Cartesian theory of knowledge come to the front. What precisely is the guarantee for the objective validity, or cor respondence to fact, of (say) our judgments of perception? In the fact of perceiving there are, according to Descartes, two ele ments involved,—a certain amount of sensuous data and an idea of the object perceived. Neither of these can be legitimately thought of as produced by any external thing supposed to corre spond to the process of perceiving and, in view of the general principle just mentioned, there are no means within the mind itself of accounting for these occurrences.

No other expedient is, therefore, available than that of resort ing to what is equally demanded by the very conception of the finite, namely, an Infinite. Briefly, Descartes' solution of the problem is that the divine power must be thought of as coordinat ing changes in the external world with perceptions of the finite mind,—a doctrine which when more fully elaborated by the later Cartesians came to bear the title Occasionalism. Stated generally, then, in Descartes' view, finite existents, whether minds or cor poreal things, must be regarded as contingent, and any proposition relating to them can refer only to possible existence. There can be but one notion which by its own nature and in vir tue of its own content indicates not only possible but necessary, and therefore actual, existence,—the notion, namely, of the Infinite.