Under Logic, Aristotle treats of the methods of arriving at general propositions, and of reasoning from them. His logic is at once the art of thinking and the instrument of thought. The completeness of our knowledge depends on the extent and completeness of our experience. His manner of reasoning is by the syllogism, an argument consisting of three propositions, such that the concluding one follows of necessity from the two premises, and of which, indeed, the whole theory of demonstration is only an example. Regarding logic as the instrument of thought, he introduces into it, as a fundamental feature, the ten categories. These predicaments are the genera to which everything may be reduced, and denote the most general of the attributes which may be assigned to a thing. [Sidenote: and metaphysics.] His metaphysics overrides all the branches of the physical sciences. It undertakes an examination of the postulates on which each one of them is founded, determining their truth or fallacy. Considering that all science must find a support for its fundamental conditions in an extensive induction from facts, he puts at the foundation of his system the consideration of the individual; in relation to the world of sense, he regards four causes as necessary for the production of a fact--the material cause, the substantial cause, the efficient cause, the final cause. [Sidenote: Temporary failure of his system.] [Sidenote: The Peripatetic philosophy.] [Sidenote: Substance, Motion, Space, Time.] [Sidenote: The world.] [Sidenote: Organic beings.] [Sidenote: Physiological conclusions.]