Vowel breaking

In historical linguistics, vowel breaking, vowel fracture, or diphthongization is the sound change of a monophthong into a diphthong or triphthong.

Types

Vowel breaking may be unconditioned or conditioned. It may be triggered by the presence of another sound, by stress, or in no particular way.

Assimilation

Vowel breaking is sometimes defined as a subtype of diphthongization, when it refers to harmonic process that involves diphthongization triggered by a following vowel or consonant.
The original pure vowel typically breaks into two segments. The first segment matches the original vowel, and the second segment is harmonic with the nature of the triggering vowel or consonant. For example, the second segment may be if the following vowel or consonant is back, and the second segment may be if the following vowel or consonant is front.
Thus, vowel breaking, in the restricted sense, can be viewed as an example of assimilation of a vowel to a following vowel or consonant.

Unconditioned

Vowel breaking is sometimes not assimilatory and is then not triggered by a neighboring sound. That was the case with the Great Vowel Shift in English in which all cases of and changed to diphthongs.

Stress

Vowel breaking sometimes occurs only in stressed syllables. For instance, Vulgar Latin open-mid and changed to diphthongs only when they were stressed.

Indo-European languages

English

Vowel breaking is a very common sound change in the history of the English language, occurring at least three times listed here in reverse chronological order:

Southern American English

Vowel breaking is characteristic of the "Southern drawl" of Southern American English, where the short front vowels have developed a glide up to , and then in some areas back down to schwa: pat, pet, pit.

Great Vowel Shift

The Great Vowel Shift changed the long vowels to diphthongs, which became Modern English.

Old English īs > Modern English ice
Old English hūs > Modern English ''house''
Middle English

In early Middle English, a vowel was inserted between a front vowel and a following , and a vowel was inserted between a back vowel and a following .
That is a prototypical example of the narrow sense of "vowel breaking" as described above: the original vowel breaks into a diphthong that assimilates to the following consonant, gaining a front before a palatal consonant and before a velar consonant.

Old English

In Old English, two forms of harmonic vowel breaking occurred: breaking and retraction and back mutation.
In prehistoric Old English, breaking and retraction changed stressed short and long front vowels i, e, æ to short and long diphthongs spelled io, eo, ea when followed by h or by r, l + another consonant, and sometimes w :

Proto-Germanic *fallan > Anglo-Frisian *fællan > Old English feallan "fall"
PG *erþō > OE eorþe "earth"
PG *lizaną > OE liornian "learn"

In late prehistoric Old English, back mutation changed short front i, e, æ to short diphthongs spelled io, eo, ea before a back vowel in the next syllable if the intervening consonant was of a certain nature. The specific nature of the consonants that trigger back umlaut or block it varied from dialect to dialect.

Old Norse

stressed short e becomes ja or jǫ regularly in Old Norse except after w, r, l. Examples are:

PG ek "I" → ON jak, Swedish jag, Danish and Norwegian Bokmål jeg, and Icelandic ek → ég.
* Faroese has both. The standard form is eg, while the dialects of Suðuroy have jeg.
PG hertōn "heart" → ON hjarta, Swedish hjärta, Faroese hjarta, Norwegian Nynorsk hjarta, Danish hjerte
PG erþō "earth" → Proto-Norse erþū → ON jǫrð, Swedish, Danish, Norwegian jord, Faroese jørð

According to some scholars, the diphthongisation of e is an unconditioned sound change, whereas other scholars speak about epenthesis or umlaut.

Faroese

Inherited Old Norse stressed long vowels and short a became diphthongs in open syllables in Modern Faroese: close and mid vowels became falling diphthongs ending in /i̯/ or /u̯/, but the open vowels a, æ and á became floating diphthongs /ɛaː/ or /ɔaː/ respectivelly:

ON faðir → Faroese faðir "father", cf. Svabo's 1773 orthography Fêaïr, Fêajir.*
ON tré → Faroese træ "tree", cf. Svabo's 1773 orthography Trêa.*
ON ǽƦ → Faroese ær "ewe", cf. Svabo's 1773 orthography Êar.*
ON bátƦ → Faroese bátur "boat", cf. Svabo's 1773 orthography Baatur.
ON þú → Faroese tú "thou; you ", cf. Svabo's 1773 orthography tû.
ON móðir → Faroese móðir "mother", cf. Svabo's 1773 orthography Mêuïr, Mêuür.*
ON íss → Faroese ísur "ice", cf. Svabo's 1773 orthography Ujsur.
ON ýsa → Faroese hýsa "haddock", cf. Svabo's 1773 orthography Hujsa.

Note: Svabo notes the diphthongs êa, êu with circumflex over both letters: e᷍a, e᷍u.
Diphthongisation of ON í and ý /ʊi/ appears also in closed syllables; ON ó, ú in closed syllable lost its diphthongal character during the beginning of the 19th century:

ON hvítt → Faroese hvítt "white ", cf. Svabo's 1773 orthography kvujt, kvujtt.
ON nýtt → Faroese nýtt "new ", cf. Svabo's 1773 orthography nujt.
ON stórt → Faroese stórt "big ", cf. Svabo's 1773 orthography stêurt, størt, Schrøter's 1822 orthography stourt.
German and Yiddish

The long high vowels of Middle High German underwent breaking during the transition to Early New High German: →. In Yiddish, the diphthongization affected the long mid vowels as well: →

MHG êwic → NHG ewig,
MHG hôch → NHG hoch,
MHG schœne → NHG schön,
MHG snîden → NHG schneiden,
MHG vriunt → NHG Freund,
MHG hût → NHG Haut,

This change started as early as the 12th century in Upper Bavarian and reached Moselle Franconian only in the 16th century. It did not affect Alemannic or Ripuarian dialects, which still retain the original long vowels.
In Yiddish, the diphthongization applied not only to MHG long vowels but also to in words of Hebrew or Slavic origin:

→
→
Old Czech: chřěn →
→
Scottish Gaelic

Vowel breaking is present in Scottish Gaelic with the following changes occurring often but variably between dialects: Archaic Irish → Scottish Gaelic and Archaic Irish → Scottish Gaelic Specifically, central dialects have more vowel breaking than others.

Romance languages

Many Romance languages underwent vowel breaking. The Vulgar Latin open vowels e and o in stressed position underwent breaking only in open syllables in French and Italian, but in both open and closed syllables in Spanish. Vowel breaking was mostly absent in Catalan, in which and became diphthongs only before a palatal consonant: Latin coxa 'thigh', octō 'eight', lectum 'bed' > Old Catalan,,. The middle vowel was subsequently lost if a triphthong was produced: Modern Catalan cuixa, vuit, llit. Vowel breaking was completely absent in Portuguese. The result of breaking varies between languages: e and o became ie and ue in Spanish, ie and uo in Italian and ie and eu in French.
In the table below, words with breaking are bolded.

Syllable shape	Latin	Spanish	French	Italian	Portuguese	Catalan
Open	petram, focum	piedra, fuego	pierre, feu	pietra, fuoco	pedra, fogo	pedra, foc
Closed	festam, portam	fiesta, puerta	fête, porte	festa, porta	festa, porta	festa, porta

Romanian

underwent the general Romance breaking only with, as it did not have :

Latin pellis > Romanian piele "skin"

It underwent a later breaking of stressed e and o to ea and oa before a mid or open vowel:

Latin porta > Romanian poartă "gate"
Latin flōs > Romanian floare "flower"

Sometimes a word underwent both forms of breaking in succession:

Latin petra > Early Romanian pietră > Romanian piatră "stone"

The diphthongs that resulted from the Romance and the Romanian breakings were modified when they occurred after palatalized consonants.

Quebec French

In Quebec French, long vowels are generally diphthongized when followed by a consonant in the same syllable.

tard → ; but not in tardif
père →
fleur → ; but not in fleuriste
fort → ; but not forte
autre → ; but not autrement
neutre → ; but not neutralité
pince → ; or → ; but not pincer
onze → ; but not ''onzième''
Proto-Indo-European

Some scholars believe that Proto-Indo-European i, u had vowel-breaking before an original laryngeal in Greek, Armenian and Tocharian but that the other Indo-European languages kept the monophthongs:

PIE gʷih₃wos → gʷioHwos "alive" → Gk. ζωός zōós, Toch. B śāw-, śāy-
PIE protih₃kʷom → protioHkʷom "front side" → Gk. πρόσωπον prósōpon "face", Toch. B pratsāko "breast"
PIE duh₂ros → duaHros "long" → Gk. δηρός dērós, Arm. *twār → erkar.

However, the hypothesis has not been widely adopted.

Austronesian languages

Some languages in Sumatra have vowel breaking processes, almost exclusively in syllable-final position. In Minangkabau, the Proto-Malayic vowels *i and *u are broken to ia and ua before word-final *h, *k, *l, *ŋ, *r. In Rejang, the Proto-Malayo-Polynesian vowels *ə, i, and u are broken to êa, ea, and oa before any of word-final consonants above except *k and *ŋ. This process has been transphonologized by loss of *l and *r and merging of several word-final consonants into a glottal stop.
Word-final Proto-Malayo-Polynesian *-i and *-u were also broken in Sumatra. In Rejang, these vowels are broken into -ai and -au in Pesisir dialect, or into -êi and -êu elsewhere.
Although Acehnese is also spoken in Sumatra, the entire Chamic family has undergone vowel breaking separately. Final open *-i and *-u were broken in Proto-Chamic into *-ɛy and *-ɔw. However, they remained when closed by another consonant. The following are the outcomes for the diphthongs:
Following its split from Proto-Chamic, several daughter languages have undergone further vowel breaking. In Acehnese, *a: normally became ɯə, but when preceded by a nasal, it became ɯ instead.