3. Umlaut.
[§ 10.] By umlaut is meant the modification (palatalization) of an accented vowel through the influence of an ī̆ or j which originally stood in the following syllable. The only vowel which underwent this change in OHG. was a, which became close e ([§ 2, note]).
The change is first met with in OHG. monuments about the middle of the eighth century. In the ninth century the process was practically complete except when the a was followed by certain consonant combinations which prevented umlaut from taking place. These consonant combinations were:—
[1.] ht, hs, or consonant + w, as maht, power, pl. mahti; wahsit, he grows, inf. wahsan; bi-scatwen from *-scatwjan, to shade.
[2.] In Upper German before l + consonant, before hh, ch (= Germanic k), and often before r + consonant, and before h (= Germanic h), as Upper German haltit beside Upper Franconian heltit, he holds, inf. haltan; UG. altiro beside UF. eltiro, older; UG. sachit beside UF. sehhit, he quarrels, inf. sachan, Goth. sakan; UG. warmen beside wermen, Goth. warmjan, to warm; UG. slahit beside slehit, he strikes, inf. OHG. slahan, Goth. slahan.
[3.] In words ending in -nissi, -nissa, or -līh, as firstantnissi, understanding; infancnissa, assumption; kraftlīh, strong; tagalīh, daily.
Umlaut must have taken place earlier in the spoken language than it is expressed in late OHG. and early MHG. manuscripts, because the ī̆ which caused the umlaut was weakened to e in MHG. ([§ 7]) and j had disappeared except between vowels. The vowels and diphthongs which underwent umlaut in MHG. are a, o, u, ā, ō, ū, ou, uo. The umlaut of all these sounds was completed by about the year 1200.
a > e: gast, guest, pl. geste (OHG. gesti); lamp, lamb, pl. lember (OHG. lembir); inf. graben, to dig, pres. second and third pers. sing. grebes(t), grebet (OHG. grebis, grebit); lanc, long, beside lenge (OHG. lengī), length; brennen, Goth. brannjan, to burn; bette (OHG. betti), bed.
a > ä: From the twelfth century onwards the umlaut of a also occurs—often beside forms without umlaut—in words containing the consonant combinations which prevented umlaut from taking place in OHG., as pl. mähte (OHG. mahti), powers; geslähte (OHG. gislahti), race, generation; wähset (OHG. wahsit), he grows; wärmen (OHG. warmen, older *warmjan), to warm; Upper German älter (OHG. altiro), older; kälte (OHG. kaltī), coldness; hältet (OHG. haltit), he holds; äher (OHG. ahir), ear of corn; slähet (OHG. slahit), he strikes. It also occurs in derivatives ending in -līch, -līn, as mänlīch, manly, schämelīch, shameful, tägelīch, daily, väterlīch, fatherly, väterlīn, dim. of vater, father. It is likewise met with in MHG. words which originally had an i in the third syllable, the vowel of the second syllable having become i by assimilation, as frävele (OHG. frafali), bold, pl. mägede (OHG. magadi), maids, pl. zäher(e) (OHG. zahari), tears. See [§ 2], Note.
o > ö: Although ö, the umlaut of o, is common in MHG. and still commoner in NHG., yet all words containing this umlaut are really new formations due to levelling or analogy, because primitive Germanic u ([§ 15]) did not become o in OHG. when followed by an ī̆ or j in the next syllable. Examples are: boc, he-goat, beside dim. böcklīn (OHG. pochilī); dorf, village, beside pl. dörfer; got, God, beside götinne, goddess; hof, court, beside hövesch, courtly; loch (OHG. loh), hole, beside pl. löcher (OHG. lohhir); tohter, daughter, beside dim. töhterlīn; pret. subj. möhte (OHG. mohti), I might; törste (OHG. torsti), I might dare.