These are not exhaustive definitions. Many other people wrote, created, and published definitions of rhetoric. What this features, however, seemed relevant to me at the moment as a marker of my journey in understanding rhetoric.
Whately: “in the present day…the province of Rhetoric, in its widest application that would be reckoned admissible, comprehends all ‘Composition in Prose’; in the narrowest sense, it would be limited to ‘Persuasive Speaking.” I propose in the present work to adopt a middle course between these two extreme points; and to treat of ‘Argumentative Composition,’ generally, and exclusively; considering Rhetoric (in conformity with the very just and philosophical view of Aristotle) as an offshoot from Logic” (832).
I think that this is interesting in terms of his description of wide and narrow rhetoric. All prose compositions (but not poetic compositions, so where on the continuum between rhetoric and poetic is Whately?) are rhetoric in its widest definition.
Whately’s description here eliminates visual rhetoric and, in my normal understanding of “composition” as something written or captured in a medium that can be re-read, eliminates speech as well. However, it is clear that Whately does not intend to eliminate speech.
Clearly Whately agrees with Aristotle that rhetoric is persuasion.
Is argumentation different than persuasion? Or is argumentation just the means by which persuasion is induced? That question seems to have potential for thought.