The textbook writers' definition is not to my liking. Amplification, they say, is language that throws greatness round its subject. But this definition can serve, of course, equally for sublimity, passion, and figurative turns, since these too throw a kind of greatness about the subject of speech. To me they seem to differ in this: that sublimity lies in elevation, amplification in mass; the former, accordingly, can lie in a single thought, while the latter always involves quantity and a certain abundance. §1
Amplification is, to define it broadly, a filling-out from all the parts and topics inherent in the subject, fortifying by sustained handling what has already been built up; and it differs from proof in this, that proof demonstrates the matter at issue […] most copiously, like an opened sea, pouring forth in many directions a far-spread greatness. §2
And so I think it stands to reason that the orator, being more passionate, has much in him of fire and an angry blaze, while the philosopher, established in dignity and lofty solemnity, is not cold but is not so violently strained. §3
It is in just these respects, dearest Terentianus, if we Greeks too may presume to judge, that Cicero differs from Demosthenes in greatness. Demosthenes is sublime in a more abrupt elevation, Cicero in copiousness; ours, by his rapidity and force and powerful skill, by his power, as it were, of burning and tearing up at once, may be likened to a thunderbolt or a lightning-flash; Cicero, like a far-spreading conflagration, ranges everywhere and rolls onward, with a great and continuing flame, kindling now here, now there, and feeding itself by succession. §4
But you will be the better judges of these matters. The right occasion of Demosthenic sublimity, of his concentrated intensity, is in passages of vehemence and strong emotion, where the hearer must above all be struck thunderstruck; the right place for the rich flow is where one needs to flood the audience: it suits commonplaces, perorations for the most part, digressions, all the descriptive and demonstrative parts, and history and natural philosophy and not a few other portions of writing. §5