He was supposed to give an account of the system of things.

But the notion of what it means to give an account of the system of things had necessarily undergone some change.

The philosopher had to be something more than a natural philosopher.
3.

PHILOSOPHY AS A GUIDE TO LIFE .-- At the close of the fourth century before Christ there arose the schools of the Stoics, the Epicureans, and the Skeptics.

In them we seem to find a somewhat new conception of philosophy--philosophy appears as chiefly a guide to life.