influence of dialectal ‑e, and its use was extended in the 19th cent. because of an idea that ‑au suggested the pl. ending.
In Ml. W. ei and eu appear in all positions, so that the mutation is not represented in writing, § 79. But ‑é-u, ‑á-u were distinct, as are contracted ‑éu, ‑áu now: diléu, parháu, § 33 iv.
(2) The mutation aw: o is not of general application. The penultimate o does not come from the ultimate aw, but both come from ɔ; see § 71 i. Hence when aw is an original diphthong < Brit. or Lat. ou or au, it remains aw in the penult, as in awdur < Lat. au(c)tōrem; so cawgiau pl. of cawg < late Lat. caucus; awydd, etc. § 76 iii; canawon, athrawon, § 36 iii. This shows nawn which gives prynhawnol, prynhawngweith, etc., to be from *nouna § 76 iii as opposed to awr which gives oriau, oriog, etc., and is from *(h)ō̦ra § 71 ii (3). In late formations aw < ā is unmutated as in mawrion § 144 iii (1), ardderchawgrwydd beside ardderchogrwydd. Before a consonant, penultimate aw is sounded əw, and sometimes written ow, as cowgiau D. 40, ardderchowgrwydd.
Where Ml. W. aw in the unaccented ult. has become o, § 71, the mutation of course disappears; thus it appears in Ml. W. pechawt, pechodeu, but is lost in Mn. W. pechod, pechodau. Where at the same time the aw represents a Brit. diphthong, as in gwrando, gwrandawaf, the rule of mutation is reversed. So in final ‑o for affected au, in athro, athrawon § 76 v (5).
(3) w appears in the penult in some words; see § 66 ii, iii. For other exceptions to mutations 4 and 5 see § 82.
(4) The mutation uw: u occurs only before ch, § 77 x. In late formations it is neglected; thus beside lluwch ‘(snow)drift’, we have the old lluchio ‘to hurl’, and the new lluwchio ‘to drive (dust or snow)’. For the derivatives of duw see § 78 iv (2).
(5) On unmutated forms in loose compounds see § 45 ii (2).
82. i. From the table in the above section it is seen that the use of the two sounds of y is regulated by the law of vowel mutation. The general rule in its special application to these sounds may be stated as follows:
y has the ɥ sound in monosyllables and final syllables, and the ỿ sound in all syllables not final; as edrɥch, edrỿchwch, brɥn, brỿniau, mỿnɥdd, wỿnỿddoedd, bỿrddau, prɥd, prỿdferth, dỿfod, cỿfỿngder.
ii. The exceptions to the rule are—
(1) A few proclitics, which, though monosyllabic, have the ỿ sound. These are ỿr, ỿ ‘the’, ỿn ‘in’, fỿ ‘my’, dỿ ‘thy’, ỿn ‘our’, ỿch ‘your’, mỿn, ỿm ‘by’ (in oaths).
Pre-verbal yẟ, yr, y (whether the relative, § 162, the affirmative particle, § 219 ii, or the conjunction, § 222 x) is now always sounded
