Poet and critic James Longenbach mapped out some interesting territory in The Art of the Poetic Line, which he expands upon in The Virtues of Poetry. In its earliest uses, he writes, the word virtue "gestured toward a magical or transcendental power," and he wants to look at poems that aspire to boldness, doubt, excess, otherness, particularity, restraint, shyness, surprise and worldliness. He seems to argue that paradox is at the heart of our best poems; they can go in two directions at the same time.
Longenbach's essays pay particular attention to the mechanics of poetry--down to the significance of stressed and unstressed syllables and the historical roots of words--as he makes the case that excellence in all kinds of poetry is fluid while at the same time exacting. Tennyson, we're told, had one of the "finest ears among poets," while Shakespeare is both "one of our greatest prose writers" and a useful tutor in writing badly. (Yeats and Pound also make frequent appearances.) Sometimes, Longenbach pairs poets to learn new things from the juxtaposition: Robert Lowell's and Elizabeth Bishop's letters to each other help explain what constitutes a confessional poem; Randall Jarrell is brought in to show us how John Ashbery is a poet both bold and shy.
In the end, Longenbach says, the origins of any poem are mysterious, but its virtues exist as the "material fact of language on the page." --Tom Lavoie, former publisher