Though the poem Sir Gawain and the Green Knight is not hard to read aloud, problems are likely to multiply as soon as one begins to think about its metre. This is because its construction is, as it were, inside out compared to the verse one is more likely to be familiar with. That verse is likely to have a fixed number of syllables to the line - or a number that at any rate can be regarded as fixed - while the number of accented points may vary. To take Paradise Lost as an example, while every line has a notional 10 syllables, the number of accents per line varies from as few as 2 to as many as 6, with 4 the most common number:

Of Mán's Fírst Disobédience, and the Frúit - etc.

In GGK, by contrast, the number of accents in each line is fixed, while the number of syllables varies.

It might seem that this kind of verse would be particularly suited to English, if, as Kenneth L. Pike famously claimed, it is a stress-timed language: one in which accents fall at more or less regular intervals however many unaccented syllables there may be between them. To the extent that this is true, however, the very fact gives a line with a fixed number of syllables and a varying number of accents a great rhythmic flexibility, since accented syllables take substantially more time than unaccented ones. This is perhaps one reason accentual verse fell out of fashion.

Rhythmic flexibility in GGK comes from variation in the position of the accent, and from variation in the number of unaccented syllables, though that latter quantity does not vary much. Each of the long lines in GGK comprises two halflines. The first halfline has two accents, which may be written with the symbol / and two unaccented strings, which may be written with the symbol x. These occur in every possible arrangement: //xx, /x/x, /xx/, x//x, x/x/ and xx//. The second halfline has two accents but only one unaccented string, and two arrangements of these occur: /x/ and x//.

Typically both accented syllables in the first halfline alliterate with the first, but not the second, accented syllable in the second halfline, though sometimes the alliteration is carried by a first, unaccented, syllable of the word containing the accent. It is not uncommon also for the first halfline to contain additional, unaccented, alliterating words.

Each unaccented string consists of a pair of unstressed syllables. Unpaired unaccented syllables do not count for metrical purposes, except when a metrically defective halfline can be made regular by understanding a notional extra syllable. This most often happens at the end of the first halfline, where the pause, as it were, stands in for a syllable. Most second halflines end with a single unstressed syllable, which is not counted metrically, any more than the eleventh syllable that ends about two thirds of Chaucer's 'pentameters'.

The examples of scansion that follow should make the principles clear:

	Siþen þe sege & þe assaut watʒ sesed at Troye,	x/x/	/x/
	Þe borʒ brittened & brent to brondeʒ & askeʒ,	x/x/	/x/
	Þe tulk þat þe trammes of tresoun þer wroʒt,	/x/x(1)	/x/
	Watʒ tried for his tricherie, þe trewest on erthe;	/x/x	/x/
5	Hit watʒ Ennias þe athel, & his highe kynde,	x/x/	x//
	Þat siþen depreced prouinces, & patrounes bicome	x//x(2)	/x/
	Welneʒe of al þe wele in þe west iles,	/xx/	x//
	Fro riche Romulus to Rome ricchis hym swyþe,	x/x/	/x/
	With gret bobbaunce þat burʒe he biges vpon fyrst,	x/x/	/x/
10	& neuenes hit his aune nome, as hit now hat;	/xx/(2)	x//
	Ticius to Tuskan & teldes bigynnes;	/x/x(1)	/x/
	Langaberde in Lumbardie lyftes vp homes;	/x/x	/x/
	& fer ouer þe French flod Felix Brutus	/xx/(3)	/x/(4)
	On mony bonkkes ful brode Bretayn he setteʒ	x/x/	/x/
	1. a single syllable before the caesura counts as 2. 2. a syllabic resonant is discounted. 3. there is more than one way to scan this a-line; of the two ways that don’t involve supplying an extra syllable, this is the commoner form. 4. a notional syllable must be supplied after ‘Felix’.