What is the purpose of terza rima?
to elevate language
to honor the classics
to move forward in reading
to aid translation of italian

  Terza rima is rhyming verse form that consists of an interlocking three-line rhime scheme. It was first used by the Italian poet Dante Alighieri. It uses a chain rhime with the pattern "ABA BCB CDC DED"  there is no limit to the number of lines but they all finished with a single line or a couplet repeating the previous middle rhime.

  The firsts known use of terza rima is in Dante´s "Divine Comedy", he may had been influenced by the lyric poetry "Sirventes" from the provençal troubadours. The three line pattern may have been intended to suggest the holy trinity, inspired by Dante other italian poets began to used it. For the english language the first poet to used it was Geoffrey Chaucer but in English is more difficult to use because of the shortage of rhime words available in the language in comparisson with the italian who has a more complex phonology.

   With all this information given I believe that the purpose of the terza rima is to move forward in reading because each "stanza" gives you a preview of what rhime is comming in the next one. Besides by being a three line rhime is a short "stanza" and keep you hooked to the poem.

  I´ll copy an examples of terza rima in english from the author Percy Bysshe Shelley and the poem is called "Ode to the West Wind":

"O wild West Wind, thou breath of Autumn's being,  A

Thou, from whose unseen presence the leaves dead  B

Are driven, like ghosts from an enchanter fleeing,          A

Yellow, and black, and pale, and hectic red,                 B

Pestilence-stricken multitudes: O thou,                         C

Who chariotest to their dark wintery bed                         B

The winged seeds, where they lie cold and low,       C

Each like a corpse within its grave, until                       D

Thine azure sister of the Spring shall blow               C    

Her clarion o'er the dreaming earth, and fill              D

Driving sweet buds like flocks to feed in air)              E

With living hues and odours plain and hill:              D

Wild Spirit, which art moving everywhere;                     E

Destroyer and preserver; hear, oh, hear!                    E "

  I hope the answer help you. Regards.

brazil   is on the caost