596 Db WHEWELL, ON PLATO'S NOTION OF DIALECTIC. 



the wise. In the next chapter, he speaks of the uses of Dialectic, which, he says, are three, 

 mental discipline, debates, and philosophical science. And he adds {Top. i. 2, 6) that it is also 

 useful with reference to the First Principles in each Science : for from the appropriate Principles 

 of each science we cannot deduce anything concerning First Principles, since these principles are 

 the beginning of reasoning. But from the probable principles in each province of science we 

 must reason concerning First Principles : and this is either the peculiar office of Dialectic, or 

 the office most appropriate to it ; for it is a process of investigation, and must lead to the 

 Principles of all methods. 



That a demonstrative science, as such, does not explain the origin of its own First 

 Principles, is undoubtedly true. Geometry does not undertake to give a reason for the Axioms, 

 Definitions, and Postulates. This has been attempted, both in ancient and in modern times, 

 by the Metaphysicians. But the Metaphysics employed on such subjects has not commonly 

 been called Dialectic. The term has certainly been usually employed rather as describing a 

 Method, than as determining the subject of investigation. Of the Faculty which appre- 

 hends First Principles, both according to Plato and to Aristotle, I will hereafter say a few 

 words. 



The object of the dichotomous process pursued in the Sophistes, and its result in each case, 

 is a Definition. Definition also was one of the main features of the inquiries pursued by 

 Socrates, Induction being the other ; and indeed in many cases Induction was a series of steps 

 which ended in Definition. And Aristotle also taught a peculiar method, the object and result 

 of which was the construction of Definitions : — namely his Categories. This method is one of 

 division, but very different from the divisions of the Sophistes. His method begins by dividing 

 the whole subject of possible inquiry into ten heads or Categories — Substance, Quantity, 

 Quality, Relation, Place, Time, Position, Habit, Action, Passion. These again are subdivided: 

 thus Quality is Habit or Disposition, Power, Affection, Form. And we have an example of 

 the application of this method to the construction of a Definition in the Ethics ; where he 

 determines Virtue to be a Habit with certain additional limitations. 



Thus the Induction of Socrates, the Dichotomy of the Eleatics, the Categories of 

 Aristotle, may all be considered as methods by which we proceed to the construction of 

 Definitions. If, by any method, Plato could proceed to the construction of a Definition, or 

 rather of an Idea, of the Absolute Realities on which First Principles depend, such a method 

 would correspond with the notion of Dialectic in the Republic. And if it was a method of 

 division like the Eleatic or Aristotelic, it would correspond with the notion of Dialectic in the 

 Phsedrus. 



That Plato's notion, however, cannot have been exactly either of these is, I think, 

 plain. The colloquial method of stimulating and testing the progress of the student in 

 Dialectic is implied, in the sequel of this discussion of the effect of scientific study. And 

 the method of Dialogue, as the instrument of instruction, being thus supposed, the continuation 

 of the account in the Republic, implies that Plato expected persons to be made dialectical by 

 the study of the exact sciences in a comprehensive spirit. After insisting on Geometry and 

 other sciences, he says {Rep. vn. § 16) : " The synoptical man is dialectical ; and he who is 

 not the one, is not the other." 



