Against the Sophists (17-18)

these things, I hold, require much study and are the task of a vigorous and imaginative mind:[*] for this, the student must not only have the requisite aptitude but he must learn the different kinds of discourse and practice himself in their use; and the teacher, for his part, must so expound the principles of the art with the utmost possible exactness as to leave out nothing that can be taught, and, for the rest, he must in himself set such an example of oratory

that the students who have taken form under his instruction and are able to pattern after him will, from the outset, show in their speaking a degree of grace and charm which is not found in others. When all of these requisites are found together, then the devotees of philosophy will achieve complete success; but according as any one of the things which I have mentioned is lacking, to this extent must their disciples of necessity fall below the mark.