Terza rima is a verse form composed of iambic tercets (three-line groupings). The rhyme scheme for this form of poetry is "aba bcb cdc, etc." The second line of each tercet sets the rhyme for the following tercet, and thus supplying the verse with a common thread, a way to link the stanzas. The only time the form changes is at the conclusion of the poem, where a single line that rhymes with the second line of the final tercet stands alone; the rhyme scene at the end of the poem looks like this: "xyx yzy z."
Dante used terza rima in his Divine Comedy; there, it has been noted, the three-line stanza may allude to the Trinity. Although the terza rima is an inflexible and strict stanza, it has been used successfully by a number of poets, including Boccaccio (Amorosa Visione), Petrarch (I Trionfi), Chaucer ("Complaint to His Lady") and several English Renaissance poets. More recently one finds terza rima employed by Lord Byron in his "Prophecy of Dante" and Shelly in "The Triumph of Life." Some modern poets who have used the form are W. H. Auden ("The Sea and the Mirror") and Archibald MacLeish ("Conquistador").
An excellent example of the terza rima occurs in Percy Bysshe Shelley's "Ode to the West Wind." Shelley employs a terza rima sonnet form for each of the five parts that make up the poem. Here is the first part of his poem:
O wild West Wind, thou breath of Autumn's being,[Adam Palmer]
Thou, from whose unseen presence the leaves dead
Are driven, like ghosts from an enchanter fleeing,
Yellow, and black, and pale, and hectic red,
Pestilence-stricken multitudes: O thou,
Who chariotest to their dark wintery bed
The winged seeds, where they lie cold and low,
Each like a corpse within its grave, until
Thine azure sister of the Spring shall blow
Her clarion o'er the dreaming earth, and fill
(Driving sweet buds like flocks to feed in air)
With living hues and odours plain and hill:
Wild Spirit, which art moving everywhere;
Destroyer and preserver; hear, oh, hear!