The dual, whether it agreed in form with the sg. or the pl., formerly preserved the effect of its old vocalic ending in the soft mutation of a following adj., as deu wyẟel vonllwm w.m. 56 ‘two bare-backed Irishmen’, y ddwy wragedd rywiogach L.G.C. 127 ‘the two women [who are] kinder’.
iii. In W. the noun has two genders only, the masculine and the feminine.
The following traces of the old neuter survive: (1) nouns of vacillating gender § 142 i.—(2) The neut. dual in Kelt. had been reformed with ‑n on the analogy of the sing., e.g. Ir. da n‑droch ‘2 wheels’; hence in W. after dau, some nouns, originally neuter, keep p‑, t‑, c- unmutated § 106 iii (4); thus dau cant or deucant ‘200’, dau tu or deutu ‘both sides’; and by analogy dau pen or deupen ‘two ends’.
Number.
§ 116. The plural of a noun is formed from the singular either by vowel change or by the addition of a termination, which may also be accompanied by vowel change. But where the singular has been formed by the addition to the stem of a singular termination, this is usually dropped in the plural, and sometimes a plural termination is substituted for it, in either case with or without change of vowel. There are thus seven different ways of deducing the pl. from the sing.: i. change of vowel; ii. addition of pl. ending; iii. addition of pl. ending with vowel change; iv. loss of sg. ending; v. loss of sg. ending with vowel change; vi substitution of pl. for sg. ending; vii. substitution of pl. for sg. ending with vowel change.
Parisyllabic Nouns.
§ 117. i. The vowel change that takes place when the pl. is formed from the sg. without the addition or subtraction of an ending is the ultimate i-affection; see § 83 ii. This was originally caused by the pl. termination ‑ī of o-stems; thus *bardos gave barẟ ‘bard’, but *bardī gave beirẟ ‘bards’; and also by ‑ī of neut. i-stems, as in mŷr ‘seas’ < *morī § 122 ii (4); possibly -ū of neut. u-stems, but original examples are doubtful. Later, when the cause of the affection had been forgotten, it came to be regarded merely as a sign of the pl., and was extended to all classes of stems.
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