Welsh: efeilliaid (soft mutation)


Senior Member

I know that the "soft" consonantal mutation occurs after certain prepositions and in many other cases when a word is preceded by something.
I was surprised to see it at the beginning of phrases, such as photo captions on the Welsh Wikipedia page about twins = gefeilliaid.

"Efeilliaid monosygotaidd."
"Efeilliaid o Landderfel yn godro."

However, another photo caption says:
"Gefeilliaid yn y groth (14 wythnos)."

Is there a rule behind this?

Diolch yn fawr.
  • Welsh_Sion

    Senior Member
    Welsh - Northern

    Gefell 'twin' is one of those awkward words which Welsh grammarians have spilt a lot of ink over. If it is preceded by the def. art. then it is fem. and suffers from soft mutation/treiglad meddal: yr efell.

    In other contexts, it depends on the sex of twin referred to: dau efell (masc.), dwy efell (fem.). You already knew dau and dwy cause TM. (Geiriadur yr Academi also lists gefeilles as a fem. form, but I personally haven't heard this.)

    Gefeilliaid 'twins' is plur. (Thorne calls this 'a dual plural') and irregularly also suffers from TM after the def. art. yr efeilliaid 'the twins'. (yr Efeilliaid = 'Gemini') ... But .. any following adjective does NOT mutate: yr efeilliaid drwg 'the bad twins'.

    In summary then, I think you might have a choice where there's no def. art. and I might well use both forms.

    Here's hoping a fellow Cymraeg user can add to the discussion ... :)


    Senior Member
    If it is preceded by the def. art. then it is fem. and suffers from soft mutation/treiglad meddal: yr efell.
    Yes, I know that singular feminine nouns undergo soft mutation after the definite article.
    My question was about the occurrence of soft mutation when there is nothing before the noun, either singular or plural.

    In summary then, I think you might have a choice where there's no def. art. and I might well use both forms.
    Is that a regular thing with feminine nouns, or is 'gefell' an exception?
    If there was a title or photo caption saying "Gardens in Wales" (no article), could that be both "Gerddi" or "Erddi yng Nghymru"?

    Gefeilliaid 'twins' is plur.
    In one of your messages you used the plural form "gefeillion". Is that a Northern variant maybe? :)


    Senior Member
    Welsh - Northern
    I included the well-known rule about SM after def. art. to fem. sing. nouns to lead into the gender discussion of dau and dwy. I know this wasn't your original question - but felt it was an interesting supplementary point. (Not many nouns do this in Cymraeg.)

    I think you're right in relation to 'gefell' being exceptional in that 'Gefeilliaid' and 'Efeilliaid' are both possible without the def. art. to indicate '(the) twins' (but NOT 'The Twins' as in 'Gemini' which must always have the def. art.). However, 'Gerddi yng Nghymru' for 'Gardens in Wales' works where '*Erddi yng Nghymru' does not. I suspect - without proof - that this might be because of this old duality which 'Gefeilliaid' shows where 'Gerddi' (as an 'ordinary' plural does not.)

    Again, with def. art. 'Y gerddi yng Nghymru' ('The gardens in Wales') works as does 'Y gefeilliaid/Yr efeilliaid yng Nghymru' ('The twins in Wales'). But '*Yr erddi yng Nghymru' for the former sentence does not.

    'Gefeilliaid' and 'gefeillion' (the latter by analogy with 'cyfaill' > 'cyfeillion' ?) both work for me as plurals (viz. 'twins') - I don't know if this is regional. GPC also lists gefyll which I guess is more poetic (= fewer syllables). Whatever, it's not part of my active vocabulary.

    Hope this is a bit clearer, but I have a tendency to go off on a few tangents sometimes and perhaps because of a legal background not always answer your question directly!

    Last edited:


    Mód ar líne
    English (Ireland)
    An interesting question! As @Welsh_Sion suspected, this is not a standard plural. It's a dual form. Dual forms take a mutation after the article.

    So, gefeilliaid must mutate to yr efeilliaid. In Geiriadur Prifysgol Cymru, it notes this, saying (yr efeilliaid, tr. deuol) [tr. deuol = the dual mutation].

    Normal plurals do not mutate after the article, which is why we have y gerddi and not yr erddi.

    Another example of this dual form mutation can be seen in the name of the mountain Yr Eifl, which is on the Llŷn Peninsula in North Wales.

    This is the dual form of the word gafl, meaning fork or groin. In Geiriadur Prifysgol Cymru it says:

    eb. ll. gaflau, deu. geifl [feminine noun, plural gaflau, dual form geifl]

    So, because geifl is a dual form, it takes a mutation after the article, and you have Yr Eifl.

    Another interesting thing about the word gefell is that because it is used so frequently in the dual form, yr efeilliaid, and people do not realise that this not a standard plural form, they don't realise that what they're dealing with is a mutated form, and so they assume that the singular form must be efell. So, by that logic, the plural form without the article must also be efeilliaid. Efell and efeilliaid are commonly used and are not considered incorrect.

    This is why you have spotted instances of both "Efeilliaid o Landderfel yn godro" and "Gefeilliaid yn y groth" online. Technically, the most correct of these is gefeilliaid.

    Personally, in spoken Welsh, I would always use efell and efeilliaid. (I speak south Wales Welsh, and I suspect this is the most common form in the south.)