THREE:However, as we have seen, he is not above turning it against Mill. The drift of his own illustration is not very clear, but we suppose it implies that the matron unconsciously frames the general proposition: My remedy is good for all children suffering from the same disease as Lucy; and with equal unconsciousness reasons down from this to the case of her neighbours child. Now, it is quite unjustifiable to call Mills analysis superficial because it leaves out of account a hypothesis incompatible with the nominalism which Mill professed. It is still more unjustifiable to quote against it390 the authority of a philosopher who perfectly agreed with those who disbelieve in the possibility of unconscious knowledge,286 and contemptuously rejected Platos opinion to the contrary. Nor is this all. The doctrine that reasoning is from particulars to particulars, even when it passes through general propositions, may be rigorously deduced from Aristotles own admissions. If nothing exists but particulars, and if knowledge is of what exists, then all knowledge is of particulars. Therefore, if the propositions entering into a chain of reasoning are knowledge, they must deal with particulars exclusively. And, quite apart from the later developments of Aristotles philosophy, we have his express assertion, that all generals are derived from particulars, which is absolutely incompatible with the alleged fact, that all knowledge, all thought, rests on universal truths, on general propositions; that all knowledge, whether deductive or inductive, is arrived at by the aid, the indispensable aid, of general propositions. To Aristotle the basis of knowledge was not truths of any kind, but concepts; and in the last chapter of the Posterior Analytics he has explained how these concepts are derived from sense-perceptions without the aid of any propositions whatever.The Academic theory of probability bears some resemblance to the Canonic of Epicurus, and may have been partially suggested by it. Both are distinguished from the Aristotelian and Stoic logic by the care with which they provide for the absence of contradictory evidence. In this point, however, the superiority of Carneades to Epicurus is very marked. It is not enough for him that a present impression should suggest a belief not inconsistent with past experience; in the true inductive spirit, he expressly searches for negative instances, and recommends the employment of experiment for this purpose. Still more philosophical is the careful and repeated analysis of attendant circumstances, a precaution not paralleled by anything in the slovenly method of his predecessor. Here the great value of scepticism as an element in mental training becomes at once apparent. The extreme fallibility of the intellectus sibi permissus had to be established before precautions could be adopted for its restraint. But the evidence accepted in proof of this fallibility has been very different at different times, and has itself given rise to more than one fallacious interpretation. With us it is, for the most part, furnished by experience. The circumstance that many demonstrable errors were formerly received as truths is quite sufficient to put us on our guard against untested opinions. With Bacon, it was not the erroneousness of previous systems, but their barrenness and immobility, which led him to question the soundness of their logic; and his doubts were confirmed by an analysis of the disturbing influences under which mens judgments are formed. The ancient Sceptics were governed entirely by priori considerations. Finding themselves confronted by an immense mass of contradictory opinions, they argued that some of these must be false as all could not possibly be true. And an analysis of the human faculties156 led them, equally on priori grounds, to the conclusion that these irreconcilable divergences were but the result and the reproduction of an interminable conflict carried on within the mind itself. They could not foresee how much time would do towards reducing the disagreement of educated opinion within a narrower compass. They did not know what the experience of experience itself would teach. And their criticisms on the logic and metaphysics of their opponents were rendered inconclusive, as against all certainty, by the extent to which they shared that logic and metaphysics themselves. Carneades, at least, seems to assume throughout that all existence is material, that there is a sharp distinction between subject and object in knowledge, and that there is an equally sharp distinction between sensation and reasoning in the processes by which knowledge is obtained. In like manner, his ethical scepticism all turns on the axiom, also shared by him with the Stoics, that for a man to be actuated by any motive but his own interest is mere folly.
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