This development is precisely parallel to that of the R-grade of ei̯ after the accent in Brit., which gave ai̯i̯ > W. ‑oeẟ, the second i̯ becoming ẟ. Similarly ou̯ after the accent gives W. ‑eü̯, prob. from ´‑ou̯u̯- § 76 iii (2).
ii. Ar. m̥̄, n̥̄ were doubtless mā, nā in Pr. Kelt. Thus Ar. *sn̥̄- (R² of √senē‑, see § 63 vii (2)), > Ir. snā-that, W. no-dwydd ‘needle’.—Ir. gnāth, W. gnawd ‘known, accustomed’ might be from *g̑n̥̄- like Lat. gnā-rus, but is more probably from *g̑nō- like Lat. nōtus, √g̑enē‑. The Gaul, ‑gnatus ‘born’ is assumed to have ā, in which case it may be from *g̑n̥̄‑; but it may have ă from ə, like W. ynad ‘judge’, Early Ml. W. pl. hyg̃neid B.B. 10, 84 < *hyn-ᵹnat < *seno-gnat- ‘elder’ < *g̑nə‑t‑, √g̑enē- ‘give birth’.
Aryan vowel gradation
§ 63. i. In Parent Aryan, while the consonants of any morphological element were comparatively stable, its vocalism varied according to circumstances; this variation is called “vowel gradation” or “ablaut”. The system is similar to, but less highly developed than, that of the Semitic languages, in which the only fixed elements of a word are its consonantal skeleton. In Aryan what may be regarded as the standard vowel was e; this is the full grade, and may be denoted by F. It interchanged with o; this grade may be denoted by F°. In either case the vowel might be lengthened, becoming ē or ō; the lengthened grades may be denoted by L and L°. The vowel might become more or less indistinct; in this case we write it below the line thus ₑ; this is the reduced grade, R. Lastly it might vanish altogether; this is the vanishing grade, V. The same syllable in different combinations may occur in any or all of these grades.
ii. Taking the root *sed- ‘sit’ as an example, the system is as follows (for z in V-grade see § 97) :
| V | R | F | F° | L | L° |
| zd | sₑd | sed | sod | sēd | sōd |
Examples: V *‑zd‑: W. nyth, Lat. nīdus, E. nest, etc. < Ar. *ni-zd-os § 97 ii, W. syth < *si‑zd‑, ibid.—R *sₑd‑: W. hadl < *sₑd-lo- § 111 vii (1).—F *sed‑: W. gorsedd ‘high seat’ < Kelt. *u̯er-en-sed‑; eistedd ‘to sit’ met. for *eitsedd < *ati-en-sed‑; Gaul. esseda ‘war-chariot’ < *en-sed‑; W. annedd ‘dwelling’ for ann-hedd < *n̥do-sed‑, cyntedd ‘porch’ < *kintu-sed‑; heddwch ‘peace’ < *sed‑; Lat. sedeo, etc.—F° *sod‑: W. hudd-ygl, Ir. suide ‘soot’ § 100 v; W. aros ‘to stay’ < *pₑri-sod‑t- § 187 iii.—L *sēd‑: Lat. sēdēs, whence W. swydd ‘office’.—L° *sōd‑: W. soddi ‘to sink’, sawdd ‘subsidence’ < *sōd‑, O.E. sōt, E. soot.
