In the authoritative Princeton Encyclopedia of Poetry and Poetics (1993), cynghanedd (harmony) is described as ‘the most sophisticated system of poetic sound-patterning practised in any poetry in the world’. Based on the complex alliterative patterns and internal rhymes found in the poetry of the Cynfeirdd and the Poets of the Princes, cynghanedd was formalized during the 14th century and is an integral part of the traditional Welsh 24 metres – the most common being the cywydd and englyn – practised by the Poets of the Gentry.
There are four main types of cynghanedd, exemplified below by quotations from poems in both Welsh and English - although cynghanedd is rarely attempted in the latter. In cynghanedd groes (cross cynghanedd) the consonants in the first part of the line are repeated in the same order in the second part:
Bara a chaws, / bir a chig (Goronwy Owen)
You silly blue-eyed / whistle-blower (Twm Morys)
Cynghanedd draws (traversing cynghanedd) is similar, but at the beginning of the second part there may be one or more unanswered consonants.
Difyr / yw gwylio defaid (Edward Huws)
We talked / (reserved) untactile (Emyr Lewis)
In cynghanedd lusg (trailing cynghanedd) the rhyme at the end of the first part of the line is repeated in the accented penultimate syllable of a polysyllabic word at the end:
Bedwyr yn drist / a distaw (T Gwynn Jones)
One brief arc / into darkness (Emyr Lewis)
Cynghanedd sain (sonorous cynghanedd) contains both rhyme and alliteration and is divided into three parts, with parts one and two rhyming, parts two and three alliterating, and obeying similar rules to cynghanedd groes and cynghanedd draws:
Lle bu’r Brython, / Saeson / sydd (anon., 15th century)
One fleeting / cementing / smile (Emyr Lewis)
The eisteddfod movement of the 18th and 19th centuries led to a renewed interest in cynghanedd, and in modern-day Wales it is still meticulously employed by a host of poets, especially in poems submitted to the chair competition at the National Eisteddfod (see awdl).