First, let us clear up the meaning of “scheme.” In this context there is no negative connotation (like “shifty” or “underhanded”). “Scheme” means “pattern” or “system” or “method.” A rhyme in a poem (meaning “repeated vowel sounds in the last syllables” – “Happy birthday to you, Many more of them, too”) gives the poem a sense of order, deliberateness, and inevitability that enhances the lines’ verisimilitude or wisdom or inevitability – gives the poem a sense of truthfulness as well as a pleasing rhythm to go along with its cadence. In literary analysis, rhyme patterns are signified by capital letters: AA, BB, CC, etc. The simplest rhyme scheme is the couplet:
(“A little knowledge is a dangerous thing; (A)
Drink deep or taste not of the Pierian spring”) (A)
The quatrain is four lines in an ABAB rhyming pattern or an XAXA pattern:
“Mary had a little lamb; (X meaning no rhyme)
Its fleece was white as snow, (A)
And everywhere that Mary went (X)
The lamb was sure to go.” (A)
There are many other more sophisticated rhyme schemes as well.
A rhyme scheme is a pattern of rhyme which is consistent through out the extent of the poem. It is often that rhyme poems get confused with rhyme schemes. If a poem is to labled with a rhyme scheme a consistent pattern must be found. Rhyme schemes are labled by their sound. Ex: a a b b c c. Each matching lettered labled out throughout the poem/scheme rhyme.