Institutio Oratoria

For although the orator's task is to speak well, rhetoric is the science of speaking well. Or if we adopt another view, the task of the artist is to persuade, while the power of persuasion resides in the art. Consequently, while it is the duty of the orator to invent and arrange, intention and arrangement may be regarded as belonging to rhetoric.

At this point there has been much disagreement, as to whether these are parts or duties of rhetoric, or, as Athenaeus believes, elements of rhetoric, which the Greeks call στοιχεῖα But they cannot correctly be called elements. For in that case we should have to regard them merely as first-principles, like the moisture, fire, matter or atoms of which the universe is said to be composed. Nor is it correct to call them duties, since they are not preformed by others, but perform something themselves. We must therefore conclude that they are parts.