Bob and wheel is the common name for a metrical device most famously used by the Pearl Poet

Pearl Poet

The "Pearl Poet", or the "Gawain Poet", is the name given to the author of Pearl, an alliterative poem written in 14th-century Middle English. Its author appears also to have written the poems Sir Gawain and the Green Knight, Patience, and Cleanness; some scholars suggest the author may also have...

 in Sir Gawain and the Green Knight

Sir Gawain and the Green Knight

Sir Gawain and the Green Knight is a late 14th-century Middle English alliterative romance outlining an adventure of Sir Gawain, a knight of King Arthur's Round Table. In the poem, Sir Gawain accepts a challenge from a mysterious warrior who is completely green, from his clothes and hair to his...

. The feature is found mainly in Middle English

Middle English

Middle English is the stage in the history of the English language during the High and Late Middle Ages, or roughly during the four centuries between the late 11th and the late 15th century....

 and Middle Scots

Middle Scots

Middle Scots was the Anglic language of Lowland Scotland in the period from 1450 to 1700. By the end of the 13th century its phonology, orthography, accidence, syntax and vocabulary had diverged markedly from Early Scots, which was virtually indistinguishable from early Northumbrian Middle English...

 poetry

Poetry

Poetry is a form of literary art in which language is used for its aesthetic and evocative qualities in addition to, or in lieu of, its apparent meaning...

, where the bob and wheel occur typically at the end of a stanza. The "bob" is a very short line, sometimes of only two syllables, followed by the "wheel," longer lines with internal rhyme

Internal rhyme

In poetry, internal rhyme, or middle rhyme, is rhyme that occurs in a single line of verse.Internal rhyme occurs in the middle of a line, as exemplified by Coleridge, "In mist or cloud, on mast or shroud" or "Whiles all the night through fog-smoke white," in "The Rime of the Ancient Mariner." ...

. There are at least forty known examples of bob and wheel use, but the origin of the form is obscure. It seems to predate the Pearl Poet.Bob and and wheel is not used mostly in all poems.

The Pearl Poet uses the bob and wheel as a transition or pivot between his alliterative verse

Alliterative verse

In prosody, alliterative verse is a form of verse that uses alliteration as the principal structuring device to unify lines of poetry, as opposed to other devices such as rhyme. The most commonly studied traditions of alliterative verse are those found in the oldest literature of many Germanic...

 and a summary/counterpoint rhyming verse, as in this example from the first stanza of the poem:

"On mony bonkkes ful brode Bretayn he settes

with wynne,

Where werre and wrake and wonder

Bi sythes has wont therinne,

And oft bothe blysse and blunder

Ful skete has skyfted synne."

The "with wynne" is an alliterative "bob," and the rhyming "wheel" (which summarizes the action) follows in the next four lines.

The matter of the bob and wheel varies, but, generally, it functions as a refrain or, at least as often, a summary or ironic counterpoint to the stanza that preceded it. Both the Anglo-Saxon use of litotes

Litotes

In rhetoric, litotes is a figure of speech in which understatement is employed for rhetorical effect when an idea is expressed by a denial of its opposite, principally via double negatives....

and the French-inspired refrain show up in the bob and wheel.

Some Modern English poets and contemporary poets have revived the use of the bob and wheel. Because of the Pearl Poet's use of the bob and wheel, numerous contemporary critical discussions treat it as a wholly regular metrical form (suggesting that it is always as the Pearl Poet uses it). In fact, in Middle English, there is great variation.