Delivery inherits the irrationality of bodily politics: naming the site where humans are most tempted to and capable of abusing their intellects for personal gain (over rational "good"). I cite Aristotle (trans. 1991) at length:
An art concerned with [the delivery of oratory] has not yet been composed, since even considerations of lexis was late in developing, and delivery seems a vulgar matter when rightly understood. But since the whole business of rhetoric is with opinion, one should pay attention to delivery, not because it is right but because it is necessary, since true justice seeks nothing more in a speech than neither to offend nor to entertain; for to contend by a means of the facts themselves is just, with the result that everything but demonstration is incidental; but nevertheless [delivery] has great power, as has been said, because of the corruption of the audience. (III.i.5) (strong added)
Here Aristotle appears at his most Platonic, echoing Socrates familar condemnation of rhetoric as empty, deceitful, and injurous in the Gorgias (trans. 1997, see specifically 457d, 459d, 463a-466). This begs the question: Why is delivery characterized as vulgarity dependent upon corruption?
Because delivery, whether lexis or hypokrisis risks tarnishing the refined and pristine rationality (the properties of invention). It is in delivery that the bare facts are most exposed to the potential sorcery of artistic proofs. Aristotle later compares delivery's effects to those of "adulterating wines" (III.ii.4), an analogy conjuring Socrates' vituperate comments on rhetoric's intoxicating and maddening effects in the Phadreus. In III.i and III.ii we find a call for transparency of language that becomes the hallmark of Enlightenment rhetoricians such as Richard Whatley and the current-traditional movement that followed them: "be sure the style does not outshine the sense." Of course, such a position causes problems for those of us who conceptualize rhetoric as more than merely either "style" or "sense" (logos) but rather as a complex (and potentially violent) interaction between style, sense, character, emotion, culture, history, politics, gender, race, psychology, excess, and desire. And more. Or less.