[230] One of the rules Descartes lays down in his posthumous art of logic, is that we ought never to busy ourselves except about objects concerning which our understanding appears capable of acquiring an unquestionable and certain knowledge, vol. xi., p. 204. This is at least too unlimited a proposition, and would exclude, not indeed all probability, but all inquiries which must by necessity end in nothing more than probability. Accordingly, we find in the next pages, that he made little account of any sciences but arithmetic and geometry, or such others as equal them in certainty. “From all this,” he concludes, “we may infer, not that arithmetic and geometry are the only sciences which we must learn, but that he who seeks the road to truth should not trouble himself with any object of which he cannot have as certain a knowledge, as of arithmetical and geometrical demonstrations.” It is unnecessary to observe what havoc this would make with investigations, even in physics, of the highest importance to mankind. Beattie, in the essay on Truth, part ii. chap. 2, has made some unfounded criticisms on the scepticism of Descartes, and endeavours to turn into ridicule his, Cogito; ergo sum. Yet if any one should deny his own, or our existence, I do not see how we could refute him, were he worthy of refutation, but by some such language; and, in fact, it is what Beattie himself says, more paraphrastically, in answering Hume. |He arrives at more certainty.| 88. The certainty of an existing Ego easily led him to that of the operations of the mind, called afterwards by Locke ideas of reflection, the believing, doubting, willing, loving, fearing, which he knew by consciousness, and indeed by means of which alone he knew that the Ego existed. He now proceeded a step farther; and reflecting on the simplest truths of arithmetic and geometry, saw that it was as impossible to doubt of them as of the acts of his mind. But as he had before tried to doubt even of these, on the hypothesis that he might be deceived by a superior intelligent power, he resolved to inquire whether such a power existed, and if it did, whether it could be a deceiver. The affirmative of the former, and the negative of the latter question Descartes established by that extremely subtle reasoning so much celebrated in the seventeenth century, but which has less frequently been deemed conclusive in later times. It is at least that which no man, not fitted by long practise for metaphysical researches, will pretend to embrace. |His proof of a Deity.|