Gwenllian's Poetry Primer

Introduction and Sources
Part I: Cynghanedd (this document!)
Part II: The 24 Forms
Part III: Examples
Appendix: A Guide to Welsh Pronunciation

Part I: Cynghanedd

Before learning the Welsh poetic forms, it's important to understand the rules of rhyme and consonantal correspondence that show up in all of them. The system used throughout Welsh poetry is called cynghanedd (king HAH neth, th as in then). Forms of cynghanedd have been present in Welsh poetry since at least the earliest surviving examples (from about the 6th century AD). Full-fledged cynghanedd became both familiar and expected in the 13th and 14th centuries.

There are three basic types of cynghanedd:

Cynghanedd Gytsain (GUT-sign)
Cynghanedd Sain (sign)
Cynghanedd Lusg (lisk)

Cynghanedd Gytsain

Cynghanedd gytsain are forms of consonantal correspondence. In all cases, each line is divided roughly in half, and consonants from the first half are repeated in the second half.

In general, I've found cynghanedd gytsain to be the most difficult to use in English. It's possible, but it takes considerable effort to find words that fit the required patterns.

There are three forms of cynghanedd gytsain:

Cynghanedd Groes (groys) (groes=cross)

In cynghanedd groes, there are two emphasized words in each line. All consonants occuring before the accented syllable of the first emphasized word are repeated in the same order before the accented syllable of the last emphasized word. It's easier seen than described:

iolau'r cwyr ilawr Caint: In this line, the emphasized words are "cwyr" and "Caint." The l and r of "iolau'r" and the c of "cwyr" are repeated in the l and r of "ilawr" and the c of "Caint."
bradwyr a droes brwydr a drwg: In this line, the emphasized words are "droes" and "drwg." The repeated pattern of consonants is b r d r d r.
Over his shire, verses ring: This line uses a couple of cheats, which we'll get to below. The emphasized words are "shire" and "ring," and the repeated consonants are v r s(h).

Cynghanedd Groes o Gyswllt (groys oh GUHS oo(l)t (see appendix for explanation of (l); groes o gyswllt=cross of connection)

This is basically the same as cynghanedd groes, except that one or more consonants are transferred (for correspondence purposes) from the first to the second half of the line. The transferred consonant belongs to both halves at once. This form is rare. Example:

gwennol deg yn ael y don: The emphasized words are "deg" and "don." The repeated pattern of consonants is g (w) n l d. The g in "deg" counts as part of the first half of the line, since it's part of the first emphasized word. At the same time, it serves as the repeated "g" at the beginning of the second half of the line.

Cynghanedd Draws (drows) (draws=across)

This is identical to cynghanedd groes, except that there are one or more "unanswered" consonants at the beginning of the second half of the line. Examples:

o Dduw ai pechawd i ddyn: "Dduw" is the first emphasized word, so the dd (pronounced like the th in "then") is the only consonant needing to be answered. The p, ch, and d don't answer any other consonants.
teilwng oedd yt gael talaith: "teilwng" is the emphasized word. Welsh words are invariably accented on the penultimate syllable, so the t and l are the only consonants needing to be answered. The dd, t, g, and l are unanswered.

Exceptions, or How to Cheat

Even in the original Welsh, there were ways to cheat. I've added one rule that I think keeps to the spirit of the Welsh rules while making things slightly easier for English.

coll n (the loss of n): It is permissible not to answer an n at the beginning of a series of correspondence.
r wreiddgoll: Never official, but an unanswered r was also fairly common.
m wreiddgoll: The same as for r, above; never official, and not quite as common.
n berfeddgoll: Again, never offical, but an n in the middle of a series was occasionally unanswered.
r berfeddgoll: Same as for n, above.
h: An h is usually not counted as a consonant for correspondence purposes, but it may be counted.
In early cynghanedd, an f could be left unanswered.
My rule for English: An "sh" may be answered by an "s," and vice versa.

Cynghanedd Sain

In cynghanedd sain, each line is divided into three parts, with two pauses. (Thus, there are three emphasized words.) The first and second parts rhyme, while the second and third are linked by consonantal correspondence. This correspondence does not have to be as complicated as any of the forms of cynghanedd groes. It may include only the last consonant before the accented syllable.

Examples:

a heddiw 'mhob lliw nid llai: In this line, the emphasized words are "heddiw," "lliw," and "llai." "heddiw" rhymes with "lliw," while the consonant ll is repeated in "lliw" and "llai."
difiau bu dechrau dychryn: In this line, "difiau," "dechrau," and "dychryn" are the emphasized words. "difiau" rhymes with "dechrau." The consonant pattern d ch r is repeated in "dechrau" and "dychryn."
Be just he must as he may: Here, "just," "must," and "may" are emphasized. "just" and "must" rhyme, while the consonant pattern h m is repeated in "he must" and "he may."

A blue marbleized line

Cynghanedd Lusg

Cynghanedd Lusg, unlike the other two types of cynghanedd, requires only rhyme and not consonantal correspondence. It is internal rhyme within the line, rather than rhyme between lines.

Each line has two emphasized words. The last word of the line must have more than one syllable and be accented on the next-to-last syllable. (Such words are very common in Welsh, where all multisyllabic words are emphasized on the next-to-last syllable. They are harder to find in English, though there are quite a few.) The final (or only) syllable of the first emphasized word, whether accented or not, rhymes with the accented syllable of the last word.

Examples:

paham y bwriai amorth: In this line, "paham" and "amorth" are the emphasized words. The (unaccented) syllable "-am" of "paham" rhymes with the (accented) syllable "am-" of "amorth."
yr haul deg ar fun neges: Here, "deg" and "neges" are the relevant words.
I hear his wise words clearly: In this English version, "hear" and "clearly" are the emphasized words.

I hope this introduction to cynghanedd has been clear. Now, continue on to Part II!