"...rhetoric is really the art of the background, and if philosophy is not the science of the background then it is nothing."
- Graham Harman
"Rhetoric is not the devious art of non-rational persuasion, but the best tool we have for exposing the unstated assumptions that lie behind any surface proposition. The analytic contempt for rhetoric and metaphor must not be emulated - not just because this attitude leads to boring results, but because it is philosophically false."
- Graham Harman
Speaking against what he calls Analytic philosophy's "knockdown arguments" that have yet to produce a Golden Age of philosophy, Graham Harman tells us that he upholds instead "hyperbolic readings of philosophers against critical ones, since critique assumes that the major problem with any piece of writing are the logical errors it contains. By contrast, to hyperbolically imagine the complete victory of any philosophy is to simulate a social environment in which it is widely held to be free of logical blunders, and hence this method allows us to focus on what Whitehead calls the 'coherence and adequacy' of that philosophy" (PN: 175). 
He goes on to tell us that he holds to the idea that a 'good rhetoric' is the key to philosophy (PN: 176): for the simple reason, that "rhetoric deals with veiled background assumptions rather than explicit dialectical figures - and if philosophy does not expose background assumptions and play counterpoint against them, then I do not know what philosophy is for (PN: 176). Instead of the logically precise yet boring precision of Analytic philosophy he admires the empowering breadth and vastness of thought within such philosophers as Plato, Spinoza, and Leibniz who "do not make fewer logical blunders than the average university professor, but are simply much vaster in adequacy, coherence, originality, relevance, and insight (PN: 176 emphais mine).
That Marshall McLuhan's work on the trivium and tetrads left a lasting impression on Harman might be a clue to his fascination with rhetoric:
"In Laws of Media, Marshall & Eric McLuhan introduce their concept of the tetrad. Every medium can be described in terms of four polarities: enhancement, obsolescence, retrieval, and reversal. In his preface to the work, Eric McLuhan boldly describes the tetrad as “the single biggest intellectual discovery not only of our time, but of at least the last couple of centuries.” Recently, he stated that he “does not retract one iota” of that brazen claim. But not only has this assertion not been accepted – it has rarely even been mocked. The tetrad has largely been ignored, even by admirers of the McLuhans. This talk will proceed under the assumption that the tetrad is, in fact, the greatest intellectual discovery of at least the last couple of centuries."
- from The Greatness of McLuhan by Graham Harman
McLuhan cites a passage from Cicero's De Oratore depicting the doctus orator, the ideal philosopher and citizen:
"Whatever the theme, from whatever art of whatever branch of knowledge it be taken, the orator, just as if he had got up the case for a client, will state it better and more gracefully than the actual discoverer and specialist."
The idea of encyclopedic knowledge was an aspect of this whole practice, and yet it was open to all for as McLuhan says, it is "not surprising, therefore, that Cicero should hold that philosophy is something that anybody can easily learn, since, like the Stoics, he held that the principles of philosophy of wisdom are innate in the hearts of all men...and that unless a man can learn a thing quickly he can never learn it at all."