THE CHANGE OF a INTO æ.
7. The occurrence of the vowel a is very much restricted. In a closed syllable, and in an open syllable followed by e(i) in the next syllable, the vowel a is mostly modified to æ; but a remains unchanged in an open syllable that is followed by a, o, or u in the next syllable. (S. § 49 f.)
Thus, dæg, dæges, dæge, ðæt, wæs, fægen, wæter; dagas, daga, dagum, faran, hafoc, wacol.
Note.—It might be supposed that the i of endings in the second weak conjugation, as in the infinitive ending -ian, would change into æ in an open syllable; but this i was originally ō, therefore words like laðian, manian, wanian, etc., constitute only an apparent exception to the rule.
THE CHANGE OF a INTO ǫ.
8. Before a nasal consonant the vowel a is changed into o. But there is no uniformity in the employment of o for a. The predominant form in EWS is o; in LWS it is a. (S. § 65.)
Thus, ǫnd, and; hǫnd, hand; lǫnd, land; mǫnig, manig; gǫngan, gangan; gesǫmnian, gesamnian.
Note.—When the preceding ǫn (< an) occurs before a voíceless spirant, f, ð, s, the nasal disappears, and, in compensation, the vowel is lengthened into ō. Under the same conditions, in and un become ī and ū. (S. §§ 66, 185.)
Thus, sōfte (< *sǫnfte), softly , tōð (< *tǫnð), tooth; ōðor (< *ǫnðor), other; gōs (< *gǫns), goose; sīð (Goth. sinþs), a going, swīð (Goth. swinþs), strong, mūð (Goth. munþs), mouth.
9. Before r+consonant, l+consonant,h+consonant, and h final, the vowels æ (from a. 7), e, i are “broken” into short diphthongs, æ becoming ea, and e, i becoming eo, io. (S. §§ 77-84.)