Institutio Oratoria

Of those who divorce eloquence from that yet fairer and more desirable title to renown, a virtuous life, some call rhetoric merely a power, some a science, but not a virtue, some a practice, some an art, though they will not allow the art to have anything in common with science or virtue, while some again call it a perversion of art or κακοτεχνία.

These persons have as a rule held that the task of oratory lies in persuasion or speaking in a persuasive manner: for this is within the power of a bad man no less than a good. Hence we get the common definition of rhetoric as the power of persuading. What I call a power, many call a capacity, and some a faculty. In order therefore that there may be no misunderstanding I will say that by power I mean δύναμις.