The only art of composition that concerns the mass of mankind, and is therefore universal in both educational practise and critical theory, is the art of effective communication by speaking and writing. This is what the ancients and most moderns call rhetoric. More ample and exact definition, though unnecessary for elementary practise, is demanded for fruitful theory; and the theory of rhetoric has always concerned so many more people than the theory of any other art as to be part of every pedagogy. Here the practise of education not only may be guided by philosophy; it must be. For any coherence in its teaching, rhetoric must be comprehended not only in its immediate functions, but in its pervasive relations to other studies. It is at once the constant in educational schemes and the art among sciences. How we are in a given time and place to learn or teach rhetoric depends on how we understand its function and scope in specific relations. The importance of a theory of rhetoric in this aspect was discerned by the greatest philosopher of antiquity. In Aristotle’s comprehensive survey of thought and action rhetoric is not merely included; it has substantive place. Aristotle’s _Rhetoric_,[1] though professedly more analytical than constructive, has a consecutive development. Neither his ethics nor his politics receives more scrutiny or shows more penetration and grasp. As if he dared not slight it, he shows in this work, comparatively brief though it is, the full reach of his intelligence. In detail it has been questioned; but in conception and plan, in direction of thought and order of presentation, it has remained fruitful. BOOK I