THREE:We have endeavoured to show that Aristotle��s account of the syllogism is redundant on the one side and defective on the other, both errors being due to a false analysis of the reasoning process itself, combined with a false metaphysical philosophy. The same evil influences tell with much greater effect on his theory of applied reasoning. Here the fundamental division, corresponding to that between heaven and earth in the cosmos, is between demonstration and dialectic or experimental reasoning. The one starts with first principles of unquestionable validity, the other with principles the validity of which is to be tested by their consequences. Stated in its most abstract form, the distinction is sound, and very nearly prefigures the modern division between deduction and induction, the process by which general laws are applied, and the process by which they are established. Aristotle, however, committed two great mistakes; he thought that each method corresponded to an entirely different order of phenomena: and he thought that both were concerned for the most part with definitions. The Posterior Analytics, which contains his theory of demonstration, answers to the astronomical portion of his physics; it is the doctrine of eternal and necessary truth. And just as his ontology distinguishes between the Prime Mover himself unmoved and the eternal movement produced by his influence, so also his logic distinguishes between infallible first principles and the truths derived from them, the latter being, in his opinion, of inferior384 value. Now, according to Aristotle, these first principles are definitions, and it is to this fact that their self-evident certainty is due. At the same time they are not verbal but real definitions��that is to say, the universal forms of things in themselves as made manifest to the eye of reason, or rather, stamped upon it like the impression of a signet-ring on wax. And, by a further refinement, he seems to distinguish between the concept as a whole and the separate marks which make it up, these last being the ultimate elements of all existence, and as much beyond its complex forms as Nous is beyond reasoned truth.

THREE: