A rhyme scheme can unite a poem and create rhythm. Some rhyme schemes simply alternate rhyming lines, while others follow a pattern for the rhyming lines, such as the popular ABBA pattern, with the first and last lines rhyming while the middle lines rhyme with each other. A rhyme scheme may continue throughout the whole poem or it may change between stanzas.
Many common poetic forms include changes in rhyme scheme between stanzas. For example, the rhyme scheme for Shakespearean sonnets is ABAB, CDCD, EFEF, GG. The poem maintains consistency with alternating rhyming lines but the specific rhymes change between stanzas. The poem ends with a rhyming couplet to make an impact. The Petrarchan, or Italian, sonnet also includes a change in rhyme scheme between stanzas. Its rhyme scheme is ABAB, ABAB, or ABBA, ABBA in the octave, then CDE, CDE, or CDC, CDC in the sestet. A CD, CD, CD pattern also may be used in the sestet. Although rhyme schemes may change between stanzas, there still is a unifying pattern throughout the poem.