Longinus, like Horace, takes a pragmatic position. His central question is, what is good writing, and how may it be achieved? His first answer is that good writing partakes of what he calls the "sublime." OK, so far that isn't terribly helpful. Good writing takes part of the good. TAUTOLOGY ALERT! TAKE COVER UNDER THE NEAREST COPY OF THE O. E. D.!
What is the sublime?
"Sublimity is a certain distinction and excellence in expression." Well . . . that's a little better, but not much. The "elevated language" of the sublime aims to cast a spell over the audience, not merely persuading but transporting the audience in an enthralling and delightful manner to the conclusion desired by the writer. So what we have seems to boil down to this: good writing partakes of the sublime, and the sublime is comprised of elevated language which takes the audience out of itself and into someplace the writer has in mind. This is still somewhat nebulous, but it gets clearer along the way.
Longinus identifies three pitfalls to avoid on the quest for sublimity:
1) Tumidity;
2) Puerility; and
3) Parenthyrsus.
Tumidity tries to "transcend the limits of the sublime" through false elevation and overblown language. Puerility (from the Latin puer--boy) is the fault Longinus associates with pedants: it is comprised of "learned trifling," a hair-splitting (often seen in the pages of College English, and anything coming out of an MLA convention) which becomes "tawdry and affected." Parenthyrsus is the expression of false, empty, or out-of-place passion, a kind of mawkish, tear-jerker sentimentality of the lowest-common-denominator sort. Longinus identifies as the source of these "ugly and parasitical growths in literature" the "pursuit of novelty in the expression of ideas." Longinus goes on to identify five elements of the sublime:
1) "the power of forming great conceptions";
2) "vehement and inspired passion";
3) "the due formation of figures";