The function of Rhetoric, then, is to deal with
things about which we deliberate, but for which we have no systematic rules; and
in the presence of such hearers as are unable to take a general view of many
stages, or to follow a lengthy chain of argument. But we only deliberate about
things which seem to admit of issuing in two ways; as for those things which
cannot in the past, present, or future be otherwise, no one deliberates about
them, if he supposes that they are such; for nothing would be gained by it.