ABSTRACT
This chapter is concerned with an Aristotelian doctrine of great historical importance. It shows that there is an important connexion between the defined symbol and the properties of that which the symbol expresses. The chapter considers what exactly is the relation between the analytic definition of a symbol and the analysis of a concept. An analytic definition of a cycloid was achieved only late in the development of mathematical theory. The traditional Logicians have formulated certain rules for framing definitions. The traditional theory of definition is based upon the theory of the predicables. Classificatory schemes in the biological sciences have been profoundly affected by the theory of organic evolution. Whilst the distinction between essential and accidental characteristics is of fundamental importance, the distinction between definition as expressing essence and propria as being demonstrable cannot be drawn in exactly the way in which Aristotle drew it.
