Rhyme Scheme

A rhyme scheme is the pattern of rhymes at the end of each line of a poem or song. It is usually referred to by using letters to indicate which lines rhyme; lines designated with the same letter all rhyme with each other.

Rhyme scheme is as integral to the structure of a text as rhythm, meter and length of phrase. Yet the way this happens seems more ambiguous than the way rhythm shapes a text, for example. Even some seasoned writers have difficulty understanding precisely how the organization of rhyme contributes to the architecture of a poem or a song.

Basically, like the other elements of writing, rhyme scheme is used to manage flow, create and relieve tension & balance, and to highlight important ideas.

Writers may choose rhyme schemes in order to:

Instead of choosing rhyme schemes haphazardly, writers can deliberately design the structure of rhyme to support their ideas.

Rhymes accelerate a text. The more times a line rhymes, the smoother the flow, and the faster it goes.

Take the most basic "AAAA" rhyme scheme for example:

There was a cat,
His name was Pat,
Outside, he sat,
And boy was he fat!

When each line ends the same way, it is smooth, and can be read quickly. Because every line rhymes, the reader doesn't slow down anywhere when they read it. If the last line was supposed to be the punchline of the poem, so to speak, then it didn't really work, because the AAAA pattern kept them reading too fast to stop at the end.

A basic distinction is between rhyme schemes that apply to a single stanza, and those that continue their pattern throughout an entire poem (see chain rhyme). There are also more elaborate related forms, like the sestina – which requires repetition of exact words in a complex pattern.

In English, highly repetitive rhyme schemes are unusual. English has more vowel sounds than Italian, for example, meaning that such a scheme would be far more restrictive for an English writer than an Italian one – there are fewer suitable words to match a given pattern. Even such schemes as the terza rima ("aba bcb cdc ded..."), used by Dante Alighieri in The Divine Comedy, have been considered too difficult for English.

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Wikipedia