The Germanic umlaut (sometimes called i-umlaut or i-mutation) is a type of linguistic umlaut in which a back vowel changes to the associated front vowel (fronting) or a front vowel becomes closer to /i/ (raising) when the following syllable contains /i/, /iː/, or /j/. It took place separately in various Germanic languages starting around 450 or 500 AD and affected all of the early languages except Gothic. An example of the resulting vowel alternation is the English plural foot ~ feet (from Germanic */fōts/, pl. */fōtiz/).
Germanic umlaut, as covered in this article, does not include other historical vowel phenomena that operated in the history of the Germanic languages such as Germanic a-mutation and the various language-specific processes of u-mutation, as well as the earlier Indo-European ablaut (vowel gradation), which is observable in the declension of Germanic strong verbs such as sing/sang/sung.
Umlaut is a form of assimilation or vowel harmony, the process by which one speech sound is altered to make it more like another adjacent sound. If a word has two vowels with one far back in the mouth and the other far forward, more effort is required to pronounce the word than if the vowels were closer together; therefore, one possible linguistic development is for these two vowels to be drawn closer together.
Germanic umlaut is a specific historical example of this process that took place in the unattested earliest stages of Old English and Old Norse and apparently later in Old High German, and some other old Germanic languages. The precise developments varied from one language to another, but the general trend was this:
- Whenever a back vowel (/a/, /o/ or /u/, whether long or short) occurred in a syllable and the front vowel /i/ or the front glide /j/ occurred in the next, the vowel in the first syllable was fronted (usually to /æ/, /ø/, and /y/ respectively). Thus, for example, West Germanic *mūsiz "mice" shifted to proto-Old English *mȳsiz, which eventually developed to modern mice, while the singular form *mūs lacked a following /i/ and was unaffected, eventually becoming modern mouse.
- When a low or mid-front vowel occurred in a syllable and the front vowel /i/ or the front glide /j/ occurred in the next, the vowel in the first syllable was raised. This happened less often in the Germanic languages, partly because of earlier vowel harmony in similar contexts. However, for example, proto-Old English /æ/ became /e/ in, for example, */bæddj-/ > /bedd/ 'bed'.
The fronted variant caused by umlaut was originally allophonic (a variant sound automatically predictable from the context), but it later became phonemic (a separate sound in its own right) when the context was lost but the variant sound remained. The following examples show how, when final -i was lost, the variant sound -ȳ- became a new phoneme in Old English:
|Loss of final -z||West Germanic||*mūs||*mūsi||*fōt||*fōti|
|Germanic umlaut||Pre-Old English||*mūs||*mȳsi||*fōt||*fø̄ti|
|Loss of i after a heavy syllable||Pre-Old English||mūs||mȳs||fōt||fø̄t|
|Unrounding of ø̄ (> ē)||Most Old English dialects||mūs||mȳs||fōt||fēt|
|Unrounding of ȳ (> ī)||Early Middle English||mūs||mīs||fōt||fēt|
|Great Vowel Shift||Early Modern and Modern English||/maʊs/ ("mouse")||/maɪs/ ("mice")||/fʊt/ ("foot")||/fiːt/ ("feet")|
Although umlaut was not a grammatical process, umlauted vowels often serve to distinguish grammatical forms (and thus show similarities to ablaut when viewed synchronically), as can be seen in the English word man. In ancient Germanic, it and some other words had the plural suffix -iz, with the same vowel as the singular. As it contained an i, this suffix caused fronting of the vowel, and when the suffix later disappeared, the mutated vowel remained as the only plural marker: men. In English, such plurals are rare: man, woman, tooth, goose, foot, mouse, louse, brother (archaic or specialized plural in brethren), and cow (poetic and dialectal plural in kine). It also can be found in a few fossilized diminutive forms, such as kitten from cat and kernel from corn, and the feminine vixen from fox. Umlaut is conspicuous when it occurs in one of such a pair of forms, but there are many mutated words without an unmutated parallel form. Germanic actively derived causative weak verbs from ordinary strong verbs by applying a suffix, which later caused umlaut, to a past tense form. Some of these survived into modern English as doublets of verbs, including fell and set vs. fall (older past *fefall) and sit. Umlaut could occur in borrowings as well if stressed vowel was coloured by a subsequent front vowel, such as German Köln, "Cologne", from Latin Colonia, or Käse, "cheese", from Latin caseus.
Parallel umlauts in some modern Germanic languages
|*fallaną - *fallijaną||fallen - fällen||to fall - to fell||vallen - vellen||falla - fälla||falla - fella|
|*fōts - *fōtiz||Fuß - Füße||foot - feet||voet - voeten (no umlaut)||fot - fötter||fótur - føtur|
|*aldaz - *alþizô - *alþistaz||alt - älter - am ältesten||old - elder - eldest||oud - ouder - oudst (no umlaut)||gammal - äldre - äldst (irregular)||gamal - eldri - elstur (irregular)|
|*fullaz - *fullijaną||voll - füllen||full - fill||vol - vullen||full - fylla||fullur - fylla|
|*langaz - *langīn/*langiþō||lang - Länge||long - length||lang - lengte||lång - längd||langur - longd|
|*lūs - *lūsiz||Laus - Läuse||louse - lice||luis - luizen (no umlaut)||lus - löss||lús - lýs|
German orthography is generally consistent in its representation of i-umlaut. The umlaut diacritic, consisting of two dots above the vowel, is used for the fronted vowels, making the historical process much more visible in the modern language than is the case in English: a>ä, o>ö, u>ü, au>äu. This is a neat solution when pairs of words with and without umlaut mutation are compared, as in umlaut plurals like Mutter - Mütter (mother, mothers).
However, in a small number of words, a vowel affected by i-umlaut is not marked with the umlaut diacritic because its origin not obvious. Either there is no unumlauted equivalent or they are not recognized as a pair because the meanings have drifted apart. The adjective fertig ("ready", "finished"; originally "ready to go") contains an umlaut mutation, but it is spelled with e rather than ä as its relationship to Fahrt (journey) has, for most speakers of the language, been lost from sight. Likewise, alt (old) has the comparative älter (older), but the noun from this is spelled Eltern (parents). Aufwand (effort) has the verb aufwenden (to spend, to dedicate) and the adjective aufwendig (requiring effort) though the 1996 spelling reform now permits the alternative spelling aufwändig (but not * aufwänden). For denken, see below.
Conversely, some foreign words have umlaut diacritics that do not mark a vowel produced by the sound change of umlaut. Notable examples are Känguru from English kangaroo, and Büro from French bureau. In the latter case, the diacritic is a pure phonological marker, with no regard to etymology; in case of the kangaroo (identical in sound to *Kenguru), it somewhat etymologically marks the fact that the sound is written with an a in English. Similarly, Big Mac can be spelt Big Mäc in German, which even used to be the official spelling used by McDonald's in Germany. In borrowings from Latin and Greek, Latin ae, oe, or Greek ai, oi, are rendered in German as ä and ö respectively (Ägypten, "Egypt", or Ökonomie, "economy"). However, Latin/Greek y is written y in German instead of ü (Psychologie); y ended up being used entirely instead of ü in Scandinavia for native words as well.
Für "for" is a special case; it is an umlauted form of vor "before", but other historical developments changed the expected ö into ü. In this case, the ü marks a genuine but irregular umlaut. Other special cases are fünf "five" (expected form *finf) and zwölf "twelve" (expected form *zwälf/zwelf), in which modern umlauted vowel arose from a different process:rounding an unrounded front vowel (possibly from the labial consonants w/f occurring on both sides).
Orthography and design history
The German phonological umlaut is present in the Old High German period and continues to develop in Middle High German. From the Middle High German, it was sometimes denoted in written German by adding an e to the affected vowel, either after the vowel or, in the small form, above it. This can still be seen in some names:Goethe, Goebbels, Staedtler.
In blackletter handwriting, as used in German manuscripts of the later Middle Ages and also in many printed texts of the early modern period, the superscript ⟨e⟩ still had a form that would now be recognisable as an ⟨e⟩, but in manuscript writing, umlauted vowels could be indicated by two dots since the late medieval period.
Unusual umlaut designs are sometimes also created for graphic design purposes, such as to fit an umlaut into tightly-spaced lines of text. It may include umlauts placed vertically or inside the body of the letter.
False ablaut in verbs
Two interesting examples of umlaut involve vowel distinctions in Germanic verbs and often are subsumed under the heading "ablaut" in descriptions of Germanic verbs, giving them the name false ablaut.
The German word Rückumlaut ("reverse umlaut") is the slightly misleading term given to the vowel distinction between present and past tense forms of certain Germanic weak verbs. Examples in English are think/thought, bring/brought, tell/told, sell/sold. (These verbs have a dental -t or -d as a tense marker; therefore, they are weak and the vowel change cannot be conditioned by ablaut.) The presence of umlaut is possibly more obvious in German denken/dachte ("think/thought"), especially if it is remembered that in German the letters ⟨ä⟩ and ⟨e⟩ are usually phonetically equivalent. The Proto-Germanic verb would have been *þankijaną; the /j/ caused umlaut in all the forms that had the suffix; subsequently, the /j/ disappeared. The term "reverse umlaut" indicates that if, with traditional grammar, the infinitive and the present tense as the starting point, there is the illusion of an undoing of umlaut (so to speak, ⟨ä⟩→⟨a⟩) in the past tense, but of course, the historical development was simply umlaut in the present tense forms and none in the past.
A variety of umlaut occurs in the second and third person singular forms of the present tense of some Germanic strong verbs. For example, German fangen ("to catch") has the present tense ich fange, du fängst, er fängt. The verb geben ("give") has the present tense ich gebe, du gibst, er gibt, but the shift e→i would not be a normal result of umlaut in German. There are, in fact, two distinct phenomena at play here; the first is indeed umlaut as it is best known, but the second is older and occurred already in Proto-Germanic itself. In both cases, a following i triggered a vowel change, but in Proto-Germanic, it affected only e. The effect on back vowels did not occur until hundreds of years later, after the Germanic languages had already begun to split up: *fą̄haną, *fą̄hidi with no umlaut of a, but *gebaną, *gibidi with umlaut of e.
In German, strong verbs which display a back vowel in the past tense undergo umlaut in the subjunctive mood: singen/sang (ind.)→sänge (subj.) ("sing/sang"); fechten/focht (ind.)→föchte (subj.) ("fight/fought"). Again, this is due to the presence of a following i in the verb endings in the Old High German period.
West Germanic languages
Although umlaut operated the same way in all the West Germanic languages, the exact words in which it took place and the outcomes of the process differ between the languages. Of particular note is the loss of word-final -i after heavy syllables. In the more southern languages (Old High German, Old Dutch, Old Saxon), forms that lost -i often show no umlaut, but in the more northern languages (Old English, Old Frisian), the forms do. Compare Old English ġiest "guest", which shows umlaut, and Old High German gast, which does not, both from Proto-Germanic *gastiz. That may mean that there was dialectal variation in the timing and spread of the two changes, with final loss happening before umlaut in the south but after it in the north. On the other hand, umlaut may have still been partly allophonic, and the loss of the conditioning sound may have triggered an "un-umlauting" of the preceding vowel. Nevertheless, medial -ij- consistently triggers umlaut although its subsequent loss is universal in West Germanic except for Old Saxon and early Old High German.
I-mutation in Old English
I-mutation generally affected Old English vowels as follows in each of the main dialects. It led to the introduction into Old English of the new sounds /y(ː)/, /ø(ː)/ (which, in most varieties, soon turned into /e(ː)/), and a sound written in Early West Saxon manuscripts as ie but whose phonetic value is debated.
|original||i-mutated||examples and notes|
|a||æ, e||æ, e > e||æ, e||bacan "to bake", bæcþ "(he/she) bakes". a > e particularly before nasal consonants: mann "person", menn "people"|
|ā||ǣ||ǣ||ǣ||lār "teaching" (cf. "lore"), lǣran "to teach"|
|æ||e||e||e||þæc "covering" (cf. "thatch"), þeccan "to cover"|
|e||i||i||i||not clearly attested due to earlier Germanic e > i before i, j|
|o||ø > e||ø > e||ø > e||Latin olium, Old English øle > ele.|
|ō||ø̄ > ē||ø̄ > ē||ø̄ > ē||fōt "foot", fø̄t > fēt "feet".|
|u||y||y > e||y||murnan "to mourn", myrnþ "(he/she) mourns"|
|ū||ȳ||ȳ > ē||ȳ||mūs "mouse", mȳs "mice"|
|ea||ie > y||e||e||eald "old", ieldra, eldra "older" (cf. "elder")|
|ēa||īe > ȳ||ē||ē||nēah "near" (cf. "nigh"), nīehst "nearest" (cf. "next")|
|eo||io > eo||io > eo||io > eo||examples are rare due to earlier Germanic e > i before i, j. io became eo in most later varieties of Old English|
|ēo||īo > ēo||īo > ēo||īo > ēo||examples are rare due to earlier Germanic e > i before i, j. īo became ēo in most later varieties of Old English|
|io||ie > y||io, eo||io, eo||*fiohtan "to fight", fieht "(he/she) fights". io became eo in most later varieties of Old English, giving alternations like beornan "to burn", biernþ "(he/she) burns"|
|īo||īe > ȳ||īo, ēo||īo, ēo||līoht "light", līehtan "illuminate". īo became ēo in most later varieties of Old English, giving alternations like sēoþan "to boil" (cf. "seethe"), sīeþþ "(he/she) boils"|
I-mutation is particularly visible in the inflectional and derivational morphology of Old English since it affected so many of the Old English vowels. Of 16 basic vowels and diphthongs in Old English, only the four vowels ǣ, ē, i, ī were unaffected by i-mutation. Although i-mutation was originally triggered by an /i(ː)/ or /j/ in the syllable following the affected vowel, by the time of the surviving Old English texts, the /i(ː)/ or /j/ had generally changed (usually to /e/) or been lost entirely, with the result that i-mutation generally appears as a morphological process that affects a certain (seemingly arbitrary) set of forms. These are most common forms affected:
- The plural, and genitive/dative singular, forms of consonant-declension nouns (Proto-Germanic (PGmc) *-iz), as compared to the nominative/accusative singular – e.g., fōt "foot", fēt "feet"; mūs "mouse", mȳs "mice". Many more words were affected by this change in Old English vs. modern English – e.g., bōc "book", bēc "books"; frēond "friend", frīend "friends".
- The second and third person present singular indicative of strong verbs (Pre-Old-English (Pre-OE) *-ist, *-iþ), as compared to the infinitive and other present-tense forms – e.g. helpan "to help", helpe "(I) help", hilpst "(you sg.) help" (cf. archaic "thou helpest"), hilpþ "(he/she) helps" (cf. archaic "he helpeth"), helpaþ "(we/you pl./they) help".
- The comparative form of some adjectives (Pre-OE *-ira < PGmc *-izǭ, Pre-OE *-ist < PGmc *-istaz), as compared to the base form – e.g. eald "old", ieldra "older", ieldest "oldest" (cf. "elder, eldest").
- Throughout the first class of weak verbs (original suffix -jan), as compared to the forms from which the verbs were derived – e.g. fōda "food", fēdan "to feed" < Pre-OE *fōdjan; lār "lore", lǣran "to teach"; feallan "to fall", fiellan "to fell".
- In the abstract nouns in þ(u) (PGmc *-iþō) corresponding to certain adjectives – e.g., strang "strong", strengþ(u) "strength"; hāl "whole/hale", hǣlþ(u) "health"; fūl "foul", fȳlþ(u) "filth".
- In female forms of several nouns with the suffix -enn (PGmc *-injō) – e.g., god "god", gydenn "goddess" (cf. German Gott, Göttin); fox "fox", fyxenn "vixen".
- In i-stem abstract nouns derived from verbs (PGmc *-iz) – e.g. cyme "a coming", cuman "to come"; byre "a son (orig., a being born)", beran "to bear"; fiell "a falling", feallan "to fall"; bend "a bond", bindan "to bind". Note that in some cases the abstract noun has a different vowel than the corresponding verb, due to Proto-Indo-European ablaut.
- The phonologically expected umlaut of /a/ is /æ/. However, in many cases /e/ appears. Most /a/ in Old English stem from earlier /æ/ because of a change called a-restoration. This change was blocked when /i/ or /j/ followed, leaving /æ/, which subsequently mutated to /e/. For example, in the case of talu "tale" vs. tellan "to tell", the forms at one point in the early history of Old English were *tælu and *tælljan, respectively. A-restoration converted *tælu to talu, but left *tælljan alone, and it subsequently evolved to tellan by i-mutation. The same process "should" have led to *becþ instead of bæcþ. That is, the early forms were *bæcan and *bæciþ. A-restoration converted *bæcan to bacan but left alone *bæciþ, which would normally have evolved by umlaut to *becþ. In this case, however, once a-restoration took effect, *bæciþ was modified to *baciþ by analogy with bacan, and then later umlauted to bæcþ.
- A similar process resulted in the umlaut of /o/ sometimes appearing as /e/ and sometimes (usually, in fact) as /y/. In Old English, /o/ generally stems from a-mutation of original /u/. A-mutation of /u/ was blocked by a following /i/ or /j/, which later triggered umlaut of the /u/ to /y/, the reason for alternations between /o/ and /y/ being common. Umlaut of /o/ to /e/ occurs only when an original /u/ was modified to /o/ by analogy before umlaut took place. For example, dohtor comes from late Proto-Germanic *dohter, from earlier *duhter. The plural in Proto-Germanic was *duhtriz, with /u/ unaffected by a-mutation due to the following /i/. At some point prior to i-mutation, the form *duhtriz was modified to *dohtriz by analogy with the singular form, which then allowed it to be umlauted to a form that resulted in dehter.
A few hundred years after i-umlaut began, another similar change called double umlaut occurred. It was triggered by an /i/ or /j/ in the third or fourth syllable of a word and mutated all previous vowels but worked only when the vowel directly preceding the /i/ or /j/ was /u/. This /u/ typically appears as e in Old English or is deleted:
- hægtess "witch" < PGmc *hagatusjō (cf. Old High German hagazussa)
- ǣmerge "embers" < Pre-OE *āmurja < PGmc *aimurjǭ (cf. Old High German eimurja)
- ǣrende "errand" < PGmc *ǣrundijaz (cf. Old Saxon ārundi)
- efstan "to hasten" < archaic øfestan < Pre-OE *ofustan
- ȳmest "upmost" < PGmc *uhumistaz (cf. Gothic áuhumists)
As shown by the examples, affected words typically had /u/ in the second syllable and /a/ in the first syllable. The /æ/ developed too late to break to ea or to trigger palatalization of a preceding velar.
I-mutation in High German
I-mutation is visible in Old High German (OHG), c. 800 AD, only on /a/, which was mutated to /e/. By then, it had already become partly phonologized, since some of the conditioning /i/ and /j/ sounds had been deleted or modified. The later history of German, however, shows that /o/ and /u/ were also affected; starting in Middle High German, the remaining conditioning environments disappear and /o/ and /u/ appear as /ø/ and /y/ in the appropriate environments.
That has led to a controversy over when and how i-mutation appeared on these vowels. Some (for example, Herbert Penzl) have suggested that the vowels must have been modified without being indicated for lack of a lack of proper symbols and/or because the difference was still partly allophonic. Others (such as Joseph Voyles) have suggested that the i-mutation of /o/ and /u/ was entirely analogical and pointed to the lack of i-mutation of these vowels in certain places where it would be expected, in contrast to the consistent mutation of /a/. Perhaps the answer is somewhere in between — i-mutation of /o/ and /u/ was indeed phonetic, occurring late in OHG, but later spread analogically to the environments where the conditioning had already disappeared by OHG (this is where failure of i-mutation is most likely). It must also be kept in mind that it is an issue of relative chronology: already early in the history of attested OHG, some umlauting factors are known to have disappeared (such as word-internal j after geminates and clusters), and depending on the age of OHG umlaut, that could explain some cases where expected umlaut is missing.
In modern German, umlaut as a marker of the plural of nouns is a regular feature of the language, and although umlaut itself is no longer a productive force in German, new plurals of this type can be created by analogy. Likewise, umlaut marks the comparative of many adjectives and other kinds of derived forms. Because of the grammatical importance of such pairs, the German umlaut diacritic was developed, making the phenomenon very visible. The result in German is that the vowels written as <a>, <o>, and <u> become <ä>, <ö>, and <ü>, and the diphthong <au> becomes <äu>: Mann/Männer ("man/men"), lang/länger ("long/longer"), Fuß/Füße ("foot/feet"), Maus/Mäuse ("mouse/mice"), Haus/Häuser ("house/houses"). On the phonetic realisation of these, see German phonology.
I-mutation in Old Saxon
In Old Saxon, umlaut is much less apparent than in Old Norse. The only vowel that is regularly fronted before an /i/ or /j/ is short /a/: gast – gesti, slahan – slehis. It must have had a greater effect than the orthography shows since all later dialects have a regular umlaut of both long and short vowels.
I-mutation in Dutch
The situation in Old Dutch is similar to the situation found in Old Saxon and Old High German. Late Old Dutch saw a merger of /u/ and /o/, causing their umlauted results to merge as well, giving /ʏ/. The lengthening in open syllables in early Middle Dutch then lengthened and lowered this short /ʏ/ to long /øː/ (spelled eu) in some words. This is parallel to the lowering of /i/ in open syllables to /eː/, as in schip ("ship") – schepen ("ships").
Later developments in Middle Dutch show that long vowels and diphthongs were not affected by umlaut in the more western dialects, including those in western Brabant and Holland that were most influential for standard Dutch. Thus, for example, where modern German has fühlen /ˈfyːlən/ and English has feel /fiːl/ (from Proto-Germanic *fōlijaną), standard Dutch retains a back vowel in the stem in voelen /ˈvulə(n)/. Thus, only two of the original Germanic vowels were affected by umlaut at all in western/standard Dutch: /a/, which became /ɛ/, and /u/, which became /ʏ/ (spelled u). As a result of this relatively sparse occurrence of umlaut, standard Dutch does not use umlaut as a grammatical marker. An exception is the noun stad "city" which has the irregular umlauted plural steden.
The more eastern dialects of Dutch, including eastern Brabantian and all of Limburgish have umlaut of long vowels, however. Consequently, these dialects also make grammatical use of umlaut to form plurals and diminutives, much as most other modern Germanic languages do. Compare vulen /vylə(n)/ and menneke "little man" from man.
North Germanic languages
I-mutation in Old Norse
The situation in Old Norse is complicated as there are two forms of i-mutation. Of these two, only one is phonologized. I-mutation in Old Norse is phonological:
- In Proto-Norse, if the syllable was heavy and followed by vocalic i (*gastiʀ > gestr, but *staði > *stað) or, regardless of syllable weight, if followed by consonantal i (*skunja > skyn). The rule is not perfect, as some light syllables were still umlauted: *kuni > kyn, *komiʀ > kømr.
- In Old Norse, if the following syllable contains a remaining Proto-Norse i. For example, the root of the dative singular of u-stems are i-mutated as the desinence contains a Proto-Norse i, but the dative singular of a-stems is not, as their desinence stems from P-N ē.
I-mutation is not phonological if the vowel of a long syllable is i-mutated by a syncopated i. I-mutation does not occur in short syllables.
|a||e (ę)||fagr (fair) / fegrstr (fairest)|
|au||ey||lauss (loose) / leysa (to loosen)|
|á||æ||Áss / Æsir|
|jú||ý||ljúga (to lie) / lýgr (lies)|
|o||ø||koma (to come) / kømr (comes)|
|ó||œ||róa (to row) / rœr (rows)|
|u||y||upp (up) / yppa (to lift up)|
|ú||ý||fúll (foul) / fýla (filth)|
|ǫ||ø||sǫkk (sank) / søkkva (to sink)|
- Cercignani, Fausto (1980). "Early "Umlaut" Phenomena in the Germanic Languages". Language. 56 (1): 126–136. doi:10.2307/412645.
- Cercignani, Fausto (1980). "Alleged Gothic Umlauts". Indogermanische Forschungen. 85: 207–213.
- Campbell, A. 1959. Old English Grammar. Oxford: Clarendon Press. §§624-27.
- Hogg, Richard M., ‘Phonology and Morphology’, in The Cambridge History of the English Language, Volume 1: The Beginnings to 1066, ed. by Richard M. Hogg (Cambridge: Cambridge University Press, 1992), pp. 67–167 (p. 113).
- Table adapted from Campbell, Historical Linguistics (2nd edition), 2004, p. 23. See also Malmkjær, The Linguistics Encyclopedia (2nd Edition), 2002, pp. 230-233.
- Ringe 2006, pp. 274, 280
- Duden, Die deutsche Rechtschreibung, 21st edition, p. 133.
- Isert, Jörg. "Fast Food: McDonald's schafft "Big Mäc" und "Fishmäc" ab" [Fast food: McDonald's abolishes "Big Mäc" and "Fishmäc"]. Welt Online (in German). Axel Springer AG. Retrieved 21 April 2012.
- In medieval German manuscripts, other digraphs could also be written using superscripts: in bluome 'flower', for example, the ⟨o⟩ was frequently placed above the ⟨u⟩, although this letter survives now only in Czech. Compare also the development of the tilde as a superscript n.
- Hardwig, Florian. "Unusual Umlauts (German)". Typojournal. Retrieved 15 July 2015.
- Hardwig, Florian. "Jazz in Town". Fonts in Use. Retrieved 15 July 2015.
- "Flickr collection: vertical umlauts". Flickr. Retrieved 15 July 2015.
- Hardwig, Florian. "Compact umlaut". Fonts in Use. Retrieved 15 July 2015.
- Campbell, A. 1959. Old English Grammar. Oxford: Clarendon Press. §§112, 190–204, 288.
- Penzl, H. (1949). "Umlaut and Secondary Umlaut in Old High German". Language. 25 (3): 223–240. JSTOR 410084.
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