In his lithe paper “Philosophical Invective,” G. E. L. Owen collects some delicious examples of abusive rhetoric among the ancients, which catches up the usual sense in which “rhetoric” and “argument” are standardly opposed and disjoined. He notes Aristotle's suggestion, for instance, in Rhetoric, of the effectiveness of mingling abuse with a little praise. Aristotle is also inclined to recognize “dialectic” or dialectical argument as sometimes akin to “eristic,” but he discourages too close a linkage. Dialectic, he says, is argumentative reasoning that proceeds “from opinions that are generally accepted.” “Demonstration” or demonstrative reasoning (in effect, “science”) obtains when “the premises from which the reasoning starts are true and primary, or are such that our knowledge of them has originally come through premises which are primary and true.” Eristic tends in the direction of an undesirable rhetoric in treating as “generally accepted” contentious premises that are not such at all.

The multiple uses of rhetoric that Aristotle notes conform pretty well to this instruction. For one thing, Aristotle repeatedly remarks that “we must not make people believe what is wrong” and, for another, he distinguishes the modes of persuasion proper (that is, argument) as “the only true constituents of the art: everything else is merely accessory,” Persuasion he takes to be “a sort of demonstration, since we are most fully persuaded when we consider a thing to have been demonstrated.” “Rhetoric,” he says, “is the counterpart of Dialectic,” and, like Dialectic, “is not bound up with a single definite class of subjects” but may (when functioning best) engage one or another of the exact sciences.