Welsh, like all the Celtic languages, has a system of mutations that help make important grammatical distinctions. They can tell us whether a sentence is positive or negative, whether something is a statement or a question and signal grammatical relations like the object of a verb. Mutations affect certain initial consonants and are caused by a variety of preceding words. 

There are three types of mutation:

The rules

At first, it can seem like the mutations system is random. However, there are a few underlying rules, which if learned, will mean you will always be able to select the correct mutation:

Rule 1: When mutating a sound, the place of articulation almost always remains the same  (or very near) across the series. E.g. P is mutated softly, nasally and aspirately under a variety of grammatical conditions, however, P can only be mutated to a sound that is articulated bilabially (i.e. with the lips). The same is true of C: below is a cross-section of the vocal track with the place of articulation for all the mutations of C.

So G is simply a voiced variant of C, and the nasal sound Ngh simply a nasal version of C.

Rule 2: In the nasal and aspirate mutations the initial voicing distinction of the radical is retained. E.g. P is a voiceless sound (i.e. you don't vibrate your voicebox to make the sound P) and mutates nasally to the voiceless nasal sound Mh, whilst B is a voiced sound and mutates nasally to the voiced sound M.

If you put your fingers over your neck where your voice box is (don’t strangle yourself, a light touch will do!) you can feel the difference between sounds we’re calling voiced and voiceless. Try saying B and then P. You should be able to feel that when you say B you can feel a vibration in your throat that you can’t feel when you say P. Try saying some words in English beginning with B in English and contrast them with words beginning with P.

Rule 3: There is a restricted set of possibilities. E.g. the aspirate sounds are all quiet scratchy sounds (i.e. voiceless fricatives). Sometimes it’s impossible to have a mutated version of a letter, e.g. there is no nasal version of Rh or Ll  (what would this sound like?). Likewise, M doesn’t mutate nasally because it is already a nasal sound.

Y Treiglad Meddal | The Soft Mutation

The soft mutation involves making sounds "louder" or “thicker”, either by voicing an unvoiced sound (e.g. C > G) or making a sound fricative (i.e. “scratchy”) (e.g. D > Dd).

Below are the consonants which involve a change in voicing (i.e. from no buzz in the voice box to a buzz):

P > B

T > D

C > G

The rest of the soft mutation series involves slightly different changes. The changes below all involve changing the place of articulation to a very similar sound:

B > F

D > Dd

M > F

The remaining three sounds change in different ways again:

Ll > l this is the change from a scratchy voiceless sound to a voiced sound (i.e. with a voice box buzz). 

Rh > R this is the change from a voiceless trilled r to a voiced trilled r.

G is an exception and doesn’t involve a sound change at all- it simply disappears.

What causes a soft mutation?

The following list isn't at all exhaustive, however, includes all the most common situations where you will need a soft mutation conversationally. The soft mutation occurs to all sound in the radical series except Rh and Ll under the following conditions:

• Feminine singular nouns with the definite article or the number one (un).

  • y + cath > y gath [the cat]

• Nouns or adjectives used predicatively or adverbially after yn.

  • Mae e'n + Cymro > Mae e'n Gymro [he is a Welshman]

• Adjectives following mor (so), rhy (too) or pur (fairly, very).

  • Mae e mor + crac > Mae e mor grac [he is so angry]

Common situations where the full soft mutation occurs (i.e. inlcuing Rh and Ll)

• Qualifiers (adjectives, nouns or verbal-nouns) used to qualify feminine singular nouns.

  • cath + bach > cath fach [small cat]

• Words immediately following the  prepositions am (for), ar (on), at (to), dan (under), dros (over), trwy (through,heb (without), hyd (until), gan (by), wrth (from), i (to), o (of) 

  • Aeth e i + Llanelli > Aeth i Lanelli [He went to Llanelli]

  • O + Caerydd mae hi'n dod yn wreiddiol > O Gaerdydd mae e'n dod yn wreiddiol [He's originally from Cardiff]

  • Ces i hwn wrth + cyngor y dref > Ces i hwn wrth gyngor y dref [I got this from the town council]

• Nouns following dau/dwy (two)

  • dau + ci > dau gi [two dogs]

  • dwy + cath > dwy gath [two cats]

• Nouns following adjectives (N.b. most adjectives follow the noun);

  • hen + dyn > hen ddyn [(an) old man]

• Nouns after the possessive adjectives dy (informal/singular [your]) and ei [his].

  • dy + partner > dy bartner [your partner]

  • ei + car > ei gar [his car]

• An object immediately following the subject (typically after conjugated verbs).

  • Gwelodd e + llyn > Gwelodd e lyn [He saw a lake]

• Verbnouns following an indirect object

  • Rhaid i mi + mynd > rhaid i mi fynd [I have to go]

• The second element in many compound words

  • Llan + Mair > Llanfair [The Parish of St Mary's]

• Inflected verbs in the interrogative and negative (also frequently, in the spoken language, the affirmative)

  • Cest ti amser > Gest ti amser? [You had time vs. Did you have time?]

  • Daeth e i'r parti > Ddaeth e ddim i'r parti [He came to the party vs. He didn't come to the party]

What causes a nasal mutation?

• Nouns following 'fy' [my]

  • fy + car > fy nghar

• Noun following 'yn' [in]*

  • Dw i'n byw yn + Caerdydd > Dw i'n byw yng Nghaerdydd

N.b. When using 'yn' not only does the following noun need to change, but also the form of 'yn' itself. Notice that they have to match in terms of place of articulation.

Yn : yn Nhrefdraeth [Trefdraeth]; yn Nerwen [Derwen]

Ym : ym Mhorth [Porth]; ym Mharri [Barri]

Yng : yng Nghaedydd [Caerdydd]; yng Ngwent [Gwent]

Yn can mean two different things and each separate meaning causes a different kind of mutation.

When yn appears before a verb or an adjective, it’s serving as a present tense particle, e.g.

1. Dw i’n canu (I’m singing)

2. Dw i’n grac (I’m angry)

In both sentences yn doesn’t mean in, it’s just appearing before something being described: an action underway (in sentence 1) and an emotional state (in sentence 2). Yn before adjectives causes a soft mutation, e.g. yn + crac > yn grac. However, yn before a verb doesn’t cause a mutation.

When yn appears before a noun or a location, i.e. something that something else can physically be inside (a preposition), then a nasal mutation is used:

Dw i’n byw yng Nghymru (I live in Wales).

 What causes an aspirate mutation?

• The possessive pronoun 'ei/'i' [her] (also 'i’w' [to her]

  • ei + tractor > ei thractor [her tractor]

  • a’i + plant > a'i phlant [her children]

  • i’w + tŷ > i'w thŷ [to her house]

  • Does neb wedi dod yma i’w + clywed > chlywed [No-one's come here to hear her]

• The numerals 'tri' [three, masculine]) and 'chwe' [six]:

  • tri + tŷ > tri thŷ [three houses]

  • chwe + cadair > chwe chadair  [six chairs]

• The adverb tra (“very”)

  • nofel tra + pwerus > nofel tra phwysig [a very powerful novel]

After certain preverbal particles

• Ni chymerodd e ddim sylw o'i gyngor [He didn't take any notice]

Note: 'ni' triggers aspirate mutation of p, t, c and soft mutation of all other consonants in the mutation series. This is known as mixed mutation. The particle 'ni' is usually omitted in speech, however, the aspirate mutation remains.

After certain conjunctions

• pen a phapur [pen and paper]

• mor hen â phechod ei hun [as old as sin itself]

• Dw i heb gael unrhyw gymorth na + cyngor > ... na chyngor [I haven't had any help or advice]

After certain prepositions: tua (about), gyda (with), â (with)

• tua phum punt ar hugain [about twenty-five pounds]

• Gyda chyffeilion [with friends]

• Mae’n anodd iawn bod yn bendant ynglyn â threfn y digwyddiad [It's quite difficult to be definite with regards to the organization of the event]