Inhistorical linguistics,vowel breaking,vowel fracture,^[1] ordiphthongization is thesound change of amonophthong into adiphthong ortriphthong.

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

Vowel breaking is sometimes defined as a subtype of diphthongization, when it refers to harmonic (assimilatory) 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/u/ (a back vowel) if the following vowel or consonant is back (such asvelar orpharyngeal), and the second segment may be/i/ (a front vowel) if the following vowel or consonant is front (such aspalatal).

Thus, vowel breaking, in the restricted sense, can be viewed as an example ofassimilation of a vowel to a following vowel or consonant.

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

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

Vowel breaking is a very common sound change in the history of the English language, occurring at least three times (with some varieties adding a fourth) listed here in reverse chronological order:

Vowel breaking is characteristic of the "Southern drawl" ofSouthern American English, where the shortfront vowels have developed a glide up to [j], and then in some areas back down to schwa:pat[pæjət],pet[pɛjət],pit[pɪjət].^[2]

TheGreat Vowel Shift changed the long vowels/iːuː/ to diphthongs, which becameModern English/aɪaʊ/.

• Old Englishīs > Modern Englishice/aɪs/
• Old Englishhūs > Modern Englishhouse/haʊs/

In earlyMiddle English, a vowel/i/ was inserted between a front vowel and a following/h/ (pronounced[ç] in this context), and a vowel/u/ was inserted between a back vowel and a following/h/ (pronounced[x] in this context).

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/i/ before apalatal consonant and/u/ before avelar consonant.

InOld 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 vowelsi, e, æ to short and long diphthongs spelledio, eo, ea when followed byh or byr, l + another consonant (short vowels only), and sometimesw (only for certain short vowels):^[3]

• Proto-Germanic*fallan > Anglo-Frisian*fællan > Old Englishfeallan "fall"
• PG*erþō > OEeorþe "earth"
• PG*lizaną > OEliornian "learn"

In late prehistoric Old English, back mutation changed short fronti, e, æ to short diphthongs spelledio, 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.

Proto-Germanic stressed shorte becomesja or (beforeu)jǫ regularly inOld Norse except afterw, r, l. Examples are:

• PG *ek(a) "I" → (east) ONjak,Swedishjag,Danish andNorwegian Bokmåljeg, andIcelandicek →ég (butJutlandicæ, a,Nynorskeg).
  • Faroese has both. The standard form iseg, while the dialects ofSuðuroy havejeg.
• PG *hertōn "heart" → ONhjarta,Swedishhjärta,Faroesehjarta,Norwegian Nynorskhjarta,Danishhjerte
• PG *erþō "earth" → Proto-Norse *erþū → ONjǫrð,Swedish,Danish,Norwegianjord,Faroesejørð

According to some scholars,^[4] the diphthongisation ofe is an unconditioned sound change, whereas other scholars speak aboutepenthesis^[5] orumlaut.^[6]

The long high vowels ofMiddle High German underwent breaking during the transition toEarly New High German:/iːyːuː/ →/aɪ̯ɔʏ̯aʊ̯/. InYiddish, the diphthongization affected the long mid vowels as well:/ɛːoːøːiːyːuː/ →/ɛɪ̯ɔɪ̯ɛɪ̯aɪ̯aɪ̯ɔɪ̯/

• MHGêwic → NHGewig,Yiddish:אייביק‎,romanized: eybik ("eternal")
• MHGhôch → NHGhoch,Yiddish:הויך‎,romanized: hoykh ("high")
• MHGschœne → NHGschön,Yiddish:שיין‎,romanized: sheyn ("nice")
• MHGsnîden → NHGschneiden,Yiddish:שנײַדן,romanized: shnaydn ("to cut")
• MHGvriunt → NHGFreund,Yiddish:פֿרײַנד‎,romanized: fraynd ("friend")
• MHGhût → NHGHaut,Yiddish:הויט,romanized: hoyt ("skin")

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/ɛːoː/ in words ofHebrew (in stressed open syllables) orSlavic origin:

• Hebrew:פסח,romanized: pésach →Yiddish:פּסח,romanized: peysekh ("Pesach")
• Hebrew:מנורה,romanized: m'norá →Yiddish:מנורה,romanized: mnoyre ("menorah")
• Old Czech:chřěn →Yiddish:כריין,romanized: khreyn ("chrain")
• Polish:kosz →Yiddish:קויש,romanized: koysh ("basket")

Vowel breaking is present in Scottish Gaelic with the following changes occurring often but variably between dialects: Archaic Irisheː → Scottish Gaeliciə and Archaic Irishoː → Scottish Gaelicuə^[7] Specifically, central dialects have more vowel breaking than others.

ManyRomance languages underwent vowel breaking. TheVulgar Latin open vowelse/ɛ/ ando/ɔ/ instressed position underwent breaking only in open syllables inFrench andItalian, but in both open and closed syllables inSpanish. Vowel breaking was mostly absent inCatalan, in which/ɛ/ and/ɔ/ became diphthongs only before a palatal consonant: Latin coxa 'thigh', octō 'eight', lectum 'bed' > Old Catalan*/kuoiʃa/,*/uoit/,*/lieit/. The middle vowel was subsequently lost if a triphthong was produced: Modern Catalan cuixa, vuit, llit (cf. Portuguese coxa, oito, leito). Vowel breaking was completely absent inPortuguese. The result of breaking varies between languages:e ando becameie andue in Spanish,ie anduo in Italian andie andeu/ø/ in French.

In the table below, words with breaking are bolded.

Romanian underwent the general Romance breaking only with/ɛ/, as it did not have/ɔ/:

• Latinpellis > Romanianpiele "skin"

It underwent a later breaking of stressede ando toea andoa before a mid or open vowel:

• Latinporta > Romanianpoartă "gate"
• Latinflōs (stemflōr-) > Romanianfloare "flower"

Sometimes a word underwent both forms of breaking in succession:

• Latinpetra > Early Romanianpietră > Romanianpiatră "stone" (whereia results from hypothetical *iea)

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

InQuebec French, long vowels are generally diphthongized when followed by a consonant in the same syllable (even when a final [ʁ] is optionally made silent).

• tard[tɑːʁ] →[tɑɔ̯ʁ]; but not intardif (because short a)
• père[pɛːʁ] →[paɛ̯ʁ]
• fleur[flœːʁ] →[flɶœ̯ʁ]; but not infleuriste (long œ is at end of syllable)
• fort[fɔːʁ] →[fɑɔ̯ʁ]; but notforte (short o)
• autre[oːtʁ̥] →[ou̯tʁ̥]; but notautrement (long o is at end of syllable)
• neutre[nøːtʁ̥] →[nøy̯tʁ̥]; but notneutralité (long ø is at end of syllable)
• pince[pɛ̃ːs] →[pãɛ̃s]; or[pẽːs] →[pẽɪ̯̃s]; but notpincer
• onze[õːz] →[õʊ̯̃z]; but notonzième

Some scholars^[8] believe thatProto-Indo-European (PIE)i, u had vowel-breaking before an originallaryngeal inGreek,Armenian andTocharian but that the other Indo-European languages kept the monophthongs:

• PIE *gʷih₃wos → *gʷioHwos "alive" →Gk.ζωόςzōós,Toch. Bśāw-, śāy- (butSkt.jīvá-,Lat.vīvus)
• PIE *protih₃kʷom → *protioHkʷom "front side" →Gk.πρόσωπονprósōpon "face",Toch. Bpratsāko "breast" (butSkt.prátīka-)
• PIE *duh₂ros → *duaHros "long" →Gk.δηρόςdērós,Arm. *twār →erkar (Skt.dūrá-,Lat.dūrus).

However, the hypothesis has not been widely adopted.

Some languages inSumatra have vowel breaking processes, almost exclusively in syllable-final position. InMinangkabau, theProto-Malayic vowels*i and*u are broken toia andua before word-final*h,*k,*l,*ŋ,*r (*təlur >*təluar >talua "egg").^[9] InRejang, theProto-Malayo-Polynesian vowels*ə,i, andu are broken toêa,ea, andoa before any of word-final consonants above except*k and*ŋ (*tənur >*tənoar >tênoa "egg").^[10] This process has beentransphonologized by loss of*l and*r and merging of several word-final consonants into aglottal stop (*p,*t,*k in Minangkabau, or*k,*h in most dialects of Rejang except Kebanagung).

Word-final Proto-Malayo-Polynesian*-i and*-u were also broken in Sumatra. In Rejang, these vowels are broken into-ai and-au inPesisir dialect, or into-êi and-êu elsewhere.^[10]

AlthoughAcehnese is also spoken in Sumatra, the entireChamic 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 (final*-r was lost in native words). The following are the outcomes for the diphthongs:^[11]

Following its split from Proto-Chamic, several daughter languages have undergone further vowel breaking. In Acehnese,*a: normally becameɯə, but when preceded by a nasal, it becameɯ instead.^[12]

• Smoothing (phonetics)
• Unpacking (linguistics)

• Crowley, Terry. (1997)An Introduction to Historical Linguistics. 3rd edition. Oxford University Press.
• Thurgood, Graham (1999).From Ancient Cham to Modern Dialects: Two Thousand Years of Language Contact and Change: With an Appendix of Chamic Reconstructions and Loanwords. Oceanic Linguistics Special Publications. University of Hawai'i Press. pp. i,iii–vii,ix–xiii,xv–xvii,1–259,261–275,277–397,399–407.ISBN 0824821319.JSTOR 20006770.