Umlaut of ou did not take place in the combination ouw = OHG. ouw, auw, West Germanic aww, primitive Germanic awj, as frouwe (OHG. frouwa, prim. Germanic *frawjō-), woman; ouwe (OHG. ouwa, auwia, prim. Germanic *a(ʒ)wjō-), meadow; frouwen (OHG. frouwen, prim. Germanic *frawjan), to rejoice, and similarly douwen, to digest, drouwen, to threaten, strouwen, to strew. Forms like fröuwen, döuwen, dröuwen, ströuwen were analogical formations due to the influence of the pres. second and third pers. singular and the preterite which regularly had umlaut; see the Author’s Historical German Grammar, § 232.
Umlaut of ou did not take place in Upper German before labials and g, as erlouben, to allow, gelouben, to believe, houbet, head, koufen, to buy, troumen, to dream, toufen, to baptize, bougen, to bend, ougen, to show, beside Middle German erlöuben, gelöuben, höubet, köufen, tröumen, töufen, böugen, öugen.
uo > üe: grüene (OHG. gruoni), green; güete (OHG. guotī), goodness; vüeȥe (OHG. fuoȥi), feet; pret. pl. subj. vüeren (OHG. fuorīm), we might go, inf. varn, to fare, go; buoch, book, dim. büechlīn; muoter, mother, dim. müeterlīn.
The MHG. Equivalents of the OHG. Vowels.
[§ 11.] OHG. had the following short vowels, long vowels, and diphthongs:—
| Short Vowels | a, e, ë, | i, | o, | u. |
| Long Vowels | ā, ē, | ī, | ō, | ū. |
| Diphthongs | ei, | ie (ia, ea), io (eo), iu. | ou (au), | uo. |
The following are the MHG. equivalents of the above simple vowels and diphthongs in accented syllables:—
[1.] The short vowels: Apart from the changes caused by umlaut, viz. a to ä, o to ö, u to ü ([§ 10]), and of ë to e before certain consonants, the OHG. short vowels remained in MHG., as
a = (1) MHG. a, as OHG. fater, father, tag, day, faran, to go = MHG. vater, tac, varn.
a = (2) MHG. ä, in words containing the consonant combinations which prevented umlaut from taking place in OHG., as OHG. mahti, powers, kaltī, coldness, ahir, ear of corn, warmen, to warm = MHG. mähte, kälte, äher, wärmen, see [§ 10].