Colloquial Welsh Morphology - Initial Consonant Mutation - Soft Mutation

The soft mutation (Welsh: treiglad meddal) is by far the most common mutation in Welsh. When words undergo soft mutation, the general pattern is that unvoiced plosives become voiced plosives, and voiced plosives become fricatives or disappear; some fricatives also change, and the full list is shown in the above table.

In some cases a limited soft mutation takes place. This differs from the full soft mutation in that words beginning with rh and ll do not mutate.

Common situations where the limited soft mutation occurs are as follows – note that this list is by no means exhaustive.

• feminine singular nouns with the definite article or the number one (un)
• nouns or adjectives used predicatively or adverbially after yn
• adjectives following mor ("so"), rhy ("too") or pur ("fairly, very")

Common situations where the full soft mutation occurs are as follows – note that this list is by no means exhaustive:

• adjectives (and nouns used genitively as adjectives) qualifying feminine singular nouns
• 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")
• nouns used with the number two (dau / dwy)
• nouns following adjectives (N.B. most adjectives follow the noun)
• nouns after the possessives dy (informal your) and ei (when it means his)
• an object immediately following the subject (typically after conjugated verbs)
• the second element in many compound words
• verb infinitives following an indirect object (e.g. rhaid i mi fynd - it is necessary to me to go)
• inflected verbs in the interrogative and negative (also frequently, in the spoken language, the affirmative)

The occurrence of the soft mutation often obscures the origin of placenames to non-Welsh-speaking visitors. For example, Llanfair is the church of Mair (Mary), and Pontardawe is the bridge on the Tawe.