It should be noted that the final six lines, the sestet, can actually be any combination of three rhymes - though it is uncommon for the sestet to be a set of three couplets.
The rhymes go as follows: A B B A // A B B A /// C D E // C D E. This division relates to content, as explained more below, and is sometimes signaled by a "volta" or "turn" in the ideas at line nine. To understand this rhyme scheme, think of the 14 lines of the sonnet divided into two parts: a set of eight lines (called the "octave") and a set of six lines (called the "sestet"). But it still has been used very effectively in English. This is the oldest and original rhyme scheme for the sonnet, but it more suited for Italian than for English, a language in which more of its words rhyme. To see an example of this rhyme scheme, look at Spenser's " One day I wrote her name upon the sand." So, this rhyme scheme simply reduces and interweaves the rhyming across the quatrains, thereby binding the set of quatrains together in the same way that internal rhymes keep the four lines of each quatrain coherent. Do you see how the rhyme of the last line of the first quatrain is the same rhyme as the first line of the second quatrain? The same is true between the second and third quatrains. Very similar to the Shakespearean rhyme scheme, the Spenserian sonnet is also divided into three quatrains and a couplet, but with this rhyming pattern: A B A B / B C B C / C D C D / EE. To see this in an example, look at the last word of each line in Shakespeare's sonnet 130 ("My mistress' eyes are nothing like the sun.") This rhyme scheme divides up the sonnet into three sets of four lines (or "quatrains"), followed by a final couplet (a pair of rhyming lines.) The rhymes appear in this order: A B A B / C D C D / E F E F. There are three rhyme schemes: the Shakespearean, the Spenserian, and the Petrarchan: It's useful to think of the 14 lines that make up a sonnet in groups, each of which is held together by words that rhyme in a certain pattern at the end of each line, as detailed below.