View source for Indo-European ablaut

{{Short description|Grammatical change of vowels in Indo-European languages}}
{{redirect|Ablaut|a general discussion of phonological alternations outside of Indo-European studies|Apophony}}
{{More footnotes needed|date=July 2009}}
{{Contains special characters|PIE}}
{{Sound change}}
In [[linguistics]], the '''Indo-European ablaut''' ({{IPAc-en|ˈ|æ|b|l|aʊ|t}} {{respell|AB|lowt}}, from [[Standard High German|German]] {{wikt-lang|de|Ablaut}} {{IPA|de|ˈaplaʊt|pron}}) is a system of [[apophony]] (regular [[vowel]] variations) in the [[Proto-Indo-European language]] (PIE).

An example of ablaut in English is the [[Germanic strong verb|strong verb]] ''s'''i'''ng, s'''a'''ng, s'''u'''ng'' and its related noun ''s'''o'''ng'', a paradigm inherited directly from the Proto-Indo-European stage of the language. Traces of ablaut are found in all modern [[Indo-European languages]], though its prevalence varies greatly.<ref>Fortson, §4.12.</ref><ref>Beekes, §12.2.1.</ref>

== History of the concept ==
The linguistic phenomenon of ablaut was first recorded by [[Sanskrit grammar]]ians in the later [[Vedic period]] (roughly 8th century BCE), and was codified by [[Pāṇini]] in his ''[[Aṣṭādhyāyī]]'' (4th century BCE), where the terms ''{{IAST|guṇa}}'' and ''[[vṛddhi|{{IAST|vṛddhi}}]]'' were used to describe the phenomena now known respectively as the ''full grade'' and ''lengthened grade''.<ref name=Burrow21>Burrow, §2.1.</ref><ref>Coulson, p. xv.</ref><ref>Whitney, p. xii.</ref>

In the context of European languages, the phenomenon was first described in the early 18th century by the Dutch linguist [[Lambert ten Kate]], in his book ''Gemeenschap tussen de Gottische spraeke en de Nederduytsche'' ("Common aspects of the [[Gothic language|Gothic]] and [[Dutch language|Dutch]] languages", 1710).<ref>Cornelis Dekker, ''The Origins of Old Germanic Studies in the Low Countries'', p.342ff.</ref><ref>Reproduced in [https://books.google.com/books?id=5NY5AAAAMAAJ&dq=Lambert+ten+Kate++Gem%C3%A9%C3%A9nschap+tussen+de+Gottische+spraeke+en+de+Nederduytsche&pg=PA18 Google Books]</ref>

The term ''[[wikt:ablaut|ablaut]]'' is borrowed from German, and derives from the noun {{wikt-lang|de|Laut}} "sound", and the prefix {{wikt-lang|de|ab-}}, which indicates movement downwards or away, or deviation from a norm; thus the literal meaning is "sound derivation".{{sfn|Kluge|1963}}{{sfn|Harper|2001}} It was coined in this sense in 1819 by the German linguist [[Jacob Grimm]] in his ''Deutsche Grammatik'',{{sfn|Trübner|1939}} though the word had been used before him.{{efn|The earliest attestation known to the main etymological dictionaries is a sole reference in a 16th-century discussion of rhetoric in a handbook of legal language by Johann Peter Zwengel (''Neu Groß Formular und vollkommlich Cantzlei Buch'', Frankfurt am Main 1568, page 3b), where it apparently refers to a lowering of voice pitch: ''In bewegung des leibs sind warzunemen die theil der stim (dauon ablaut) sich darnach zubewegen'' (When moving the body it is important to adjust the voice (lowering it) accordingly).<ref>Reproduced in [https://books.google.com/books?id=xkFLAAAAcAAJ&q=ablaut Google Books]</ref> Zwengel's name was misprinted as Zweigel by Schoppe, and the error has been copied in etymological dictionaries to the present day.{{sfn|Schoppe|1923}}{{sfn|Kluge|1963}}{{sfn|Harper|2001}}}} In particular, the 17th-century grammarian [[Justus Georg Schottelius|Schottelius]] had used the word negatively to suggest that German verbs lacked the sophistication of the classics,{{efn|In 1673, Schottelius used both ''ablaut'' and the adjective ''ablautend'' in his ''Horrendum bellum grammaticale Teutonum antiquissimorum'' (Horrendous grammatical war of the ancient Teutons, e.g. page 43 or page 90).<ref>Reproduced in [https://books.google.com/books?id=K_9lAAAAcAAJ&q=ungleichfliessend Google Books].</ref> His usage comes closer to that of Grimm than Zwengel's, referring to a variety of phonemic irregularities, including in what he called "ungleichfließende Verben" (i.e. strong verbs). However the connotation is negative, implying degenerate sounds: ''Wil man nun diesen so alten Isländischen Uhrkunden Glauben beilegen, dan ergibt sichs, woher in Wandagischen Zeiten den Teutschen, und sonderlich dem Teutschen Pöbelvolke, sei das Maul so krum und voll geworden, und die Zunge und Lippen so scheef und knobbicht gewachsen, daß man so unartig, ablautend und übel sprechen und ausreden müssen'' ("If these old Icelandic documents are to be believed, it seems that in the time of the folk migrations the mouths of the Germans, and especially of the rabble, had grown so twisted and full and their tongues and lips so squint and knobbly that they had to speak and enunciate in such an unschooled, degenerate (''ablautend'') and distasteful manner", page 90).

Schoppe compares this to words like "Abschaum, Abraum, Abwurf", where the ''ab-'' prefix is derogatory in the sense of "low-grade". Schoppe questions whether Grimm would have been aware of Schottelius's usage.{{sfn|Schoppe|1923}}}} but there is no hint of this disdain in Grimm or in modern scholarly usage.

In English, the term became established through the 1845 translation of [[Franz Bopp|Bopp]]'s ''Comparative Grammar''.{{efn|A translator's footnote reads: "In our language, it seems to us that the uncouthness of such compounds as Upsound, Offsound, and Insound, could hardly be compensated by any advantage to be derived from their use; and we therefore purpose, in the course of this work, where any of these terms occur in the original, to retain them in their German shape. Of these terms, Ablaut and Umlaut are those which chiefly, if not alone, are used by our author."{{sfn|Harper|2001}}}}

==Ablaut and vowel gradation==
{{further|Apophony}}
Vowel gradation is any vowel difference between two related words (such as ''ph'''o'''tograph'' {{IPA|[ˈf'''oʊ'''təgrɑːf]}} and ''ph'''o'''tography'' {{IPA|[f'''ə'''ˈtɒgrəfi]}}) or two forms of the same word (such as ''m'''a'''n'' and ''m'''e'''n''). The difference does not need to be indicated in the spelling. There are many kinds of vowel gradation in English and other languages, which are discussed generally in the article [[apophony]]. Some involve a variation in vowel length (quantitative gradation: ''ph'''o'''tograph'' / ''ph'''o'''tography'' shows reduction of the first vowel to a [[schwa]]), others in vowel coloring (qualitative gradation: ''m'''a'''n'' / ''m'''e'''n'') and others the complete disappearance of a vowel (reduction to zero: ''could n'''o'''t'' → ''couldn't'').

For the study of European languages, one of the most important instances of vowel gradation is the Indo-European ablaut, remnants of which can be seen in the English verbs ''r'''i'''de'', ''r'''o'''de'', ''r'''i'''dden'', or ''fl'''y''''', ''fl'''ew''''', ''fl'''ow'''n''. For simply learning English grammar, it is enough to note that these verbs are [[irregular verb|irregular]], but understanding why they have unusual forms that seem irregular (and indeed why they are actually perfectly regular within their own terms) requires an understanding of the grammar of the [[Reconstructed language|reconstructed proto-language]].

Ablaut is the oldest and most extensive single source of vowel gradation in the Indo-European languages and must be distinguished clearly from other forms of gradation, which developed later, such as [[Germanic Umlaut|Germanic umlaut]] (''m'''a'''n'' / ''m'''e'''n'', ''g'''oo'''se'' / ''g'''ee'''se'', ''l'''o'''ng'' / ''l'''e'''ngth'') or the results of modern English word-stress patterns (''m'''a'''n'' / ''wom'''a'''n'', ''ph'''o'''tograph'' / ''ph'''o'''tography''). Confusingly, in some contexts, the terms 'ablaut', 'vowel gradation', 'apophony' and 'vowel alternation' are used synonymously, especially in [[wikt:synchronic|synchronic]] comparisons, but [[historical linguistics|historical linguists]] prefer to keep 'ablaut' for the specific Indo-European phenomenon, which is the meaning intended by the linguists who first coined the word.

==Ablaut grades==
In Proto-Indo-European, the basic, inherent vowel of most syllables was a short ''e''. ''Ablaut'' is the name of the process whereby this short ''e'' changed, becoming short ''o'', long ''ē'', long ''ō'' or sometimes disappearing entirely to leave no vowel at all.

Thus, ablaut results in the alternation of the following sounds:

{| class="wikitable"
! zero
! short
! long
|-
| rowspan=2 | ∅
| e
| ē
|-
| o
| ō
|}

If a syllable had a short ''e'', it is said to be in the "e-grade" or "full grade". When it had no vowel, it is said to be in the "zero grade". Syllables with long vowels are said to be in "lengthened grade". (When the ''e''-grade or the ''o''-grade is referred to, the short vowel forms are meant.)

A classic example of the five grades of ablaut in a single root is provided by the different case forms of two closely related Greek words. In the following table, an acute accent (´) marks the syllable carrying the word stress; a macron (¯) marks long vowels and the syllable in '''bold''' is the one illustrating the different vowel gradations.

{| class="wikitable"
|-
! '''Ablaut grade'''
! '''PIE'''<br />(reconstruction)
! '''Greek'''
! '''Greek'''<br />(transliterated)
! '''English<br />translation'''
|-
| e-grade or<br/>full grade
| {{lang|ine-x-proto|ph₂-'''tér'''-m̥}}
| {{nowrap|{{lang|grc|πα-'''τέρ'''-α}}}}
| {{transliteration|grc|pa-'''tér'''-a}}
| "father"<br/>(noun, accusative)
|-
| lengthened<br/>e-grade
| {{lang|ine-x-proto|ph₂-'''tḗr'''}}
| {{nowrap|{{lang|grc|πα-'''τήρ'''}}}}
| {{transliteration|grc|pa-'''tḗr'''}}
| "father"<br/>(noun, nominative)
|-
| zero-grade
| {{lang|ine-x-proto|ph₂-'''tr'''-és}}
| {{nowrap|{{lang|grc|πα-'''τρ'''-ός}}}}
| {{transliteration|grc|pa-'''tr'''-ós}}
| "father's"<br/>(noun, genitive)
|-
| o-grade
| {{lang|ine-x-proto|n̥-péh₂-'''tor'''-m̥}}
| {{nowrap|{{lang|grc|ἀ-πά-'''τορ'''-α}}}}
| {{transliteration|grc|a-pá-'''tor'''-a}}
| "fatherless"<br/>(adjective, accusative)
|-
| lengthened<br/>o-grade
| {{lang|ine-x-proto|n̥-péh₂-'''tōr'''}}
| {{nowrap|{{lang|grc|ἀ-πά-'''τωρ'''}}}}
| {{transliteration|grc|a-pá-'''tōr'''}}
| "fatherless"<br/>(adjective, nominative)
|-
|}

In this unusually neat example, the following can be seen:
*A switch to the zero-grade when the word stress moves to the following syllable.
*A switch to the o-grade when the word stress moves to the preceding syllable.
*A lengthening of the vowel when the syllable is in word-final position before a sonorant.

As with most reconstructions, however, scholars differ about the details of this example.

One way to think of this system is to suppose that Proto-Indo-European originally had only one vowel, short ''e'', and over time, it changed according to phonetic context, so the language started to develop a more complex vowel system. Thus, it has often been speculated that an original e-grade underwent two changes in some phonetic environments: under certain circumstances, it changed to ''o'' (the o-grade) and in others, it disappeared entirely (the zero-grade).

However, that is not certain: the phonetic conditions that controlled ablaut have never been determined, and the position of the word stress may not have been a key factor at all.{{Citation needed|date=July 2013}} There are many counterexamples to the proposed rules: {{lang|ine-x-proto|deywós}} and its nominative plural {{lang|ine-x-proto|deywóes}} show pretonic and posttonic e-grade, respectively, and  {{lang|ine-x-proto|wĺ̥kʷos}} has an accented zero grade.

===Lengthened grades===
Many examples of lengthened grades, including those listed above, are not directly conditioned by ablaut. Instead, they are a result of sound changes like [[Szemerényi's law]] and [[Stang's law]], which caused [[compensatory lengthening]] of originally short vowels. In the examples above, Szemerényi's law affected the older sequences {{lang|ine-x-proto|ph₂-tér-s}} and {{lang|ine-x-proto|n̥-péh₂-tor-s}}, changing them to {{lang|ine-x-proto|ph₂-tḗr}} and {{lang|ine-x-proto|n̥-péh₂-tōr}}. Thus, these forms were originally in the regular, unlengthened e-grade and o-grade. Such lengthened vowels were, however, later [[grammaticalization|grammaticalised]] and spread to other words in which the change did not occur.

Nevertheless, there are examples of true lengthened grades, in which short ''e'' alternates with long ''ē''. Examples are the verbs with [[Narten present|"Narten" inflection]], and nouns like {{lang|ine-x-proto|mḗh₁-n̥s}} "moon", genitive {{lang|ine-x-proto|méh₁-n̥s-os}}. Alternations of this type were rare, however, and the ''e'' ~ ''o'' ~ ''∅'' alternation was the most common by far. The long ''ō'' grade was rarer still and may not have actually been a part of the ablaut system at all.

===Zero grade===
The zero grade of ''ablaut'' may appear difficult for speakers of English. In the case of {{lang|ine-x-proto|ph₂trés}}, which may already have been pronounced something like {{IPA|[pɐtrés]}}, it is not difficult to imagine it as a contraction of an older {{lang|ine-x-proto|ph₂terés}}, pronounced perhaps {{IPA|[pɐterés]}}, as this combination of consonants and vowels would be possible in English as well. In other cases, however, the absence of a vowel strikes the speaker of a modern western European language as unpronounceable.

To understand, one must be aware that there were a number of sounds that were consonants in principle but could operate in ways analogous to vowels: the four syllabic sonorants, the three [[laryngeal theory|laryngeals]] and the two semi-vowels:

*The [[syllabic consonant|syllabic sonorants]] are ''m'', ''n'', ''r'' and ''l'', which could be consonants much as they are in English, but they could also be held on as continuants and carry a full syllable stress and then are transcribed with a small circle beneath them. There are many modern languages who show these sounds in syllable nuclei, including Indo-European ones (e.g. [[Czech language|Czech]]). In English, these only occur very marginally in stressed position (e.g. the interjection ''hmm''), but are common [[allophone]]s of [[schwa]] when unstressed (e.g. in the second syllables of ''prison'', ''rhythm'', ''little'' etc.); there are no direct counterparts, however.
*The laryngeals could be pronounced as consonants, in which case they were probably variations on the ''h'' sound and so normally transcribed as h₁, h₂ and h₃. However, they could also carry a syllable stress, in which case they were more like vowels. Thus, some linguists prefer to transcribe them ə₁, ə₂ and ə₃. The vocalic pronunciation may have originally involved the consonantal sounds with a very slight schwa before and/or after the consonant.
*In pre-vocalic positions, the phonemes ''u'' and ''i'' were semi-vowels, probably pronounced like English ''w'' and ''y'', but they could also become pure vowels when the following ablaut vowel reduced to zero.

When ''u'' and ''i'' came in postvocalic positions, the result was a diphthong. Ablaut is nevertheless regular and looks like this:

{| class="wikitable"
|-
! e-grade
! o-grade
! zero-grade
|-
| ey
| oy
| i
|-
| ew
| ow
| u
|}

Thus, any of these could replace the ablaut vowel when it was reduced to the zero-grade: the pattern CVrC (for example, {{lang|ine-x-proto|bʰergʰ-}}) could become CrC ({{lang|ine-x-proto|bʰr̥gʰ-}}).

However, not every PIE syllable was capable of forming a zero grade; some consonant structures inhibited it in particular cases, or completely. Thus, for example, although the [[preterite]] plural of a Germanic strong verb (see below) is derived from the zero grade, classes 4 and 5 have instead vowels representing the lengthened e-grade, as the stems of these verbs could not have sustained a zero grade in this position.{{Citation needed|date=October 2016}}

Zero grade is said to be from [[pre-Proto-Indo-European]] [[syncope (phonetics)|syncope]] in unaccented syllables,{{Citation needed|date=January 2013}} but in some cases the lack of accent does not cause zero grade: {{lang|ine-x-proto|deywó-}}, nominative plural {{lang|ine-x-proto|-es}} "god". There does not seem to be a rule governing the unaccented syllables that take zero grade and the ones that take stronger grades.{{Citation needed|date=July 2013}}

===a-grade===
It is still a matter of debate whether PIE had an original a-vowel at all. In later PIE, the disappearance of the laryngeal h₂ could leave an a-colouring and this may explain all occurrences of ''a'' in later PIE. However, some argue controversially that the e-grade could sometimes be replaced by an a-grade without the influence of a laryngeal, which might help to explain the vowels in class 6 [[Germanic strong verb|Germanic verbs]], for example.

==Subsequent development==
Although PIE had only this one, basically regular, ablaut sequence, the development in the daughter languages is frequently far more complicated, and few reflect the original system as neatly as Greek. Various factors, such as [[vowel harmony]], assimilation with nasals, or the effect of the presence of laryngeals in the Indo-European (IE) roots as well as their subsequent loss in most daughter languages, mean that a language may have several different vowels representing a single vowel in the parent language.

In particular, the zero grade was often subject to modification from changes in the pronunciation of syllabic sonorants. For example, in Germanic, syllabic sonorants acquired an [[epenthesis|epenthetic]] ''-u-'', thus converting the original zero grade to a new "u-grade" in many words. Thus, while ablaut survives in some form in all Indo-European languages, it became progressively less systematic over time.

Ablaut explains vowel differences between related words of the same language. For example:
* English ''strike'' and ''stroke'' both come from the same IE root {{lang|ine-x-proto|streyg-}}. The former comes from the e-grade, the latter from the o-grade.
* German {{lang|de|Berg}} (mountain, hill) and {{lang|de|Burg}} (castle) both come from the root {{lang|ine-x-proto|bʰergʰ-}}, which presumably meant "high". The former comes from the e-grade, the latter from the zero-grade. (Zero-grade followed by ''r'' becomes ''ur'' in Germanic.)
Ablaut also explains vowel differences between cognates in different languages.
*English ''tooth'' comes from Germanic {{lang|gem-x-proto|tanþ-s}} (e.g. Old English {{lang|ang|tōþ}}, Old High German {{lang|goh|zand}}), genitive {{lang|gem-x-proto|tund-iz}} (Gothic {{transliteration|got|tunþus}}, but also {{Transliteration|got|aiƕa-tundi}} "thornbush", literally "horse-tooth"). This form is related to Latin {{lang|la|dens}}, {{lang|la|dentis}} and Greek {{lang|grc|ὀδούς}}, {{lang|grc|ὀδόντος}}, with the same meaning, and is reflected in the English words ''dentist'' and ''orthodontic''. One reconstructed IE form is {{lang|ine-x-proto|dónts}}, genitive {{lang|ine-x-proto|dn̥tés}}. The consonant differences can be explained by regular sound shifts in primitive Germanic but not the vowel differences: by the regular laws of sound changes, Germanic ''a'' can originate from PIE ''o'', but ''un'' usually goes back to a syllabic ''n̥''.

:The explanation is that the Germanic and Greek nominative forms developed from the o-grade, the Latin word and the Germanic genitive from the zero-grade (in which syllabic ''n̥'' developed into ''en'' much in the same way as it became ''un'' in Germanic). Going a step further back, some scholars reconstruct {{lang|ine-x-proto|h₁dónts}}, from the zero grade of the root {{lang|ine-x-proto|h₁ed-}} 'to eat' and the participle {{lang|ine-x-proto|-ont-}} and explain it as 'the eating one'.
*English ''foot'' comes from the lengthened o-grade of {{lang|ine-x-proto|ped-}}. Greek {{lang|grc|πούς}}, {{lang|grc|ποδός}} and Latin {{lang|la|pes}}, {{lang|la|pedis}} (compare English ''octopus'' and ''pedestrian''), come from the (short) o-grade and the e-grade respectively.

For the English-speaking non-specialist, a good reference work for quick information on IE roots, including the difference of ''ablaut'' grade behind related lexemes, is [[Calvert Watkins|Watkins]] (2000).<ref>{{cite book |editor-first=Calvert |editor-last=Watkins |editor-link=Calvert Watkins |year=2000 |orig-year=1985 |title=The American Heritage Dictionary of Indo-European Roots |edition=2nd |place=Boston, MA / New York, NY |publisher=Houghton Mifflin Harcourt |isbn=978-039598610-3 }}</ref> (Note that in discussions of lexis, Indo-European roots are normally cited in the e-grade, without any inflections.)

==Grammatical function==
In PIE, there were already ablaut differences within the paradigms of verbs and nouns. These were not the main markers of grammatical form, since the inflection system served this purpose, but they must have been significant secondary markers.

An example of ablaut in the paradigm of the noun in PIE can be found in {{lang|ine-x-proto|pértus}}, from which the English words ''ford'' and (via Latin) ''port'' are derived (both via the zero-grade stem {{lang|ine-x-proto|pr̥t-}}).

{| class="wikitable"
|-
!
!
! root (p-r)
! suffix (t-u)
|-
! Nominative
| {{lang|ine-x-proto|pér-tu-s}}
| e-grade
| zero-grade
|-
! Accusative
| {{lang|ine-x-proto|pér-tu-m}}
| e-grade
| zero-grade
|-
! Genitive
| {{lang|ine-x-proto|pr̥-téw-s}}
| zero-grade
| e-grade
|-
! Dative
| {{lang|ine-x-proto|pr̥-téw-ey}}
| zero-grade
| e-grade
|}

An example in a verb is {{lang|ine-x-proto|bʰeydʰ-}} "to wait" (cf. "bide").

{| class="wikitable"
|-
|
|
| e-grade
|
|-
| Perfect (third-person singular)
| {{lang|ine-x-proto|bʰe-bʰóydʰ-e}}
| o-grade
| (note [[reduplication|reduplicating]] prefix)
|-
| Perfect (third plural)
| {{lang|ine-x-proto|bʰe-bʰidʰ-ḗr}}
| zero-grade
| (note reduplicating prefix)
|}

In the daughter languages, these came to be important markers of grammatical distinctions. The vowel change in the Germanic strong verb, for example, is the direct descendant of that seen in the Indo-European verb paradigm. Examples in modern English are the following:

{| class="wikitable"
|-
! [[Infinitive]]
! [[Preterite]]
! [[Past participle]]
|-
| ''sing''
| ''sang''
| ''sung''
|-
| ''give''
| ''gave''
| ''given''
|-
| ''drive''
| ''drove''
| ''driven''
|-
| ''break''
| ''broke''
| ''broken''
|-
|}

It was in this context of Germanic verbs that ''ablaut'' was first described, and this is still what most people primarily associate with the phenomenon. A fuller description of ''ablaut'' operating in English, German and Dutch verbs and of the historical factors governing these can be found at the article [[Germanic strong verb]].

The same phenomenon is displayed in the verb tables of [[Latin]], [[Greek language|Ancient Greek]] and [[Sanskrit]]. Examples of ''ablaut'' as a grammatical marker in Latin are the vowel changes in the perfect stem of verbs.

{| class="wikitable"
|-
| [[Present tense]]
| [[perfect (grammar)|Perfect]]
|
|
|-
| {{lang|la|agō}}
| {{lang|la|ēgī}}
| "to do"
|
|-
| {{lang|la|videō}}
| {{lang|la|vīdī}}
| "to see"
| (vowel lengthening)
|-
| {{lang|la|sedeō}}
| {{lang|la|sēdī}}
| "to sit"
| (vowel lengthening)
|-
|}

Ablaut can often explain apparently random irregularities. For example, the verb "to be" in Latin has the forms {{lang|la|est}} (he is) and {{lang|la|sunt}} (they are). The equivalent forms in German are very similar: {{lang|de|ist}} and {{lang|de|sind}}. The same forms were present in [[Proto-Slavic]]:<ref>[[Rick Derksen|Derksen, Rick]], ''Etymological Dictionary of the Slavic Inherited Lexicon'', 2008, p. 146.</ref> {{lang|sla-x-proto|estь}} and {{lang|sla-x-proto|sǫtь}}, and developed into e.g. Polish {{lang|pl|jest}} and {{lang|pl|są}}.

The difference between singular and plural in these languages is easily explained: the PIE root is {{lang|ine-x-proto|h₁es-}}. In the singular, the stem is stressed, so it remains in the e-grade, and it takes the inflection {{lang|ine-x-proto|-ti}}. In the plural, however, the inflection {{lang|ine-x-proto|-énti}} was stressed, causing the stem to reduce to the zero grade: {{lang|ine-x-proto|h₁es-énti}} → {{lang|ine-x-proto|h₁s-énti}}. See main article: [[Indo-European copula]].

Some of the morphological functions of the various grades are as follows:

e-grade:
* Present tense of thematic verbs; root stress.
* Present singular of athematic verbs; root stress.
* Accusative and vocative singular, nominative, accusative and vocative dual, nominative plural of nouns.

o-grade:
* Verbal nouns
# stem-stressed masculine action nouns (Greek {{transliteration|grc|gónos}} "offspring", Sanskrit {{transliteration|sa|jánas}} "creature, person"; Greek {{transliteration|grc|trókhos}} "circular course" < "*act of running");
# ending-stressed feminine, originally collective, action nouns (Greek {{transliteration|grc|gonḗ}} "offspring", Sanskrit {{transliteration|sa|janā́}} "birth");
# ending-stressed masculine agent nouns (Greek {{transliteration|grc|trokhós}} "wheel" < "*runner").
* Nominative, vocative and accusative singular of certain nouns ([[Proto-Indo-European nominals#Athematic and thematic nominals|acrostatic]] root nouns such as {{lang|ine-x-proto|dṓm}}, plural {{lang|ine-x-proto|dómes}} "house"; [[Proto-Indo-European nominals#Athematic and thematic nominals|proterokinetic]] neuter nouns such as {{lang|ine-x-proto|wódr̥}} "water" or {{lang|ine-x-proto|dóru}} "tree").
* Present tense of causative verbs; stem (not root) stress.
* Perfect singular tense.

zero-grade:
* Present dual and plural tense of athematic verbs; ending stress.
* Perfect dual and plural tense; ending stress.
* Past participles; ending stress.
* Some verbs in the aorist (the Greek thematic "second aorist").
* Oblique singular/dual/plural, accusative plural of nouns.

lengthened grade:
* Nominative singular of many nouns.
* Present singular of certain athematic verbs (so-called ''Narten-stem verbs'').
* Some verbs in the aorist.
* Some derived verbal nouns (so-called ''proto-vrddhi'').

Many examples of lengthened-grade roots in the daughter languages are actually caused by the effect of [[laryngeal theory|laryngeals]] and of [[Szemerényi's law]] and [[Stang's law]], which operated within Indo-European times.

==See also==
{{columns-list|colwidth=30em|
* [[Augment (Indo-European)|Augment]]
* [[Apophony]]
* [[Germanic umlaut]]
* [[Guṇa#Sanskrit grammar|Guna (in grammar)]]
* [[I-mutation]]
* [[Inflected language]]
* [[Reduplication]]
* [[Semitic root]]
* [[Vrddhi]]
}}

==Notes==
{{notelist}}

==References==
{{Reflist|20em}}

==Bibliography==
* {{cite book | first=Robert S. P. | last=Beekes | author-link=Robert S. P. Beekes | title=Comparative Indo-European Linguistics: An Introduction | location=[[Amsterdam]] | publisher=John Benjamins | year=1995 | isbn=90-272-2150-2  |id=(Europe), (U.S.)}}
* {{cite book |last1=Fortson |first1=Benjamin W |author-link1=Benjamin W. Fortson IV|title=Indo-European Language and Culture |year=2010 |publisher=Wiley-Blackwell |isbn=978-1-4051-8895-1 |edition=2010}} 
* {{cite book |last1=Burrow |first1=Thomas | author-link1=Thomas Burrow| title=The Sanskrit Language |year=2001 |publisher=Motilal Banarsidass |isbn=81-208-1767-2 |edition=2001}}
* {{cite book |last1=Whitney |first1=William Dwight | author-link1=William Dwight Whitney|title=Sanskrit Grammar |date=January 2008 |publisher=Motilal Banarsidass |isbn=978-81-208-0620-7 |edition=2000}}
* {{cite book |last1=Coulson |first1=Michael |title=Sanskrit |year=2003 |publisher=McGraw Hill |isbn=0-340-85990-3 |edition=2003}}
* {{cite book | last=Coetsem | first=Frans van | author-link = Frans Van Coetsem | title=Ablaut and Reduplication in the Germanic Verb (=Indogermanische Bibliothek. vol 3) | year=1993 | publisher=Winter Verlag | location=Heidelberg | isbn=3-8253-4267-0}}
* {{Cite web |url=https://www.etymonline.com/word/ablaut#etymonline_v_46 |title=ablaut (n.) |access-date=2022-04-21 |website=Online Etymological Dictionary (Etymonline) |last=Harper |first=Douglas|date=2001}}
* {{Cite book |title=Etymologisches Wörterbuch der deutschen Sprache |last=Kluge |first=Friedrich |year=1963 |pages=3 |publisher=Walter de Gruyter GmbH & Co KG |isbn=9783111698847 |url=https://books.google.com/books?id=XmaEDwAAQBAJ&dq=J.P.+Zweigel+Ablaut&pg=PA3 |edition=19}}
* {{cite book | last=Kuryłowicz | first=Jerzy | author-link=Jerzy Kuryłowicz |author2=Manfred Mayrhofer |author2-link=Manfred Mayrhofer | title=Indogermanische Grammatik | year=1968–1969 | publisher=Winter Verlag| location=Heidelberg | isbn=3-533-03487-9}}
* {{cite book | last = Meier-Brügger | first = Michael | title = Indogermanische Sprachwissenschaft | year = 2002 | publisher = de Gruyter | isbn = 3-11-017243-7}}
* {{Cite journal |title=Nomina ante res |journal=Germanisch-Romanische Monatsschrift |last=Schoppe |first=Georg |volume=XI |year=1923 |pages=182–185}}
* {{cite book | last = Szemerényi | first = Oswald J. L. | author-link = Oswald Szemerényi | title = Introduction to Indo-European Linguistics | year=1996 | publisher = Oxford University Press | location = Oxford | isbn = 0-19-824015-5}}
* {{Cite book |title=Deutsches Wörterbuch |last=Trübner |first=Karl |year=1939 |language=de |url=https://books.google.com/books?id=AE7gZKgoLNsC&dq=J.P.+Zweigel+Formularbuch&pg=PA18 |issue=1|page=18|publisher=Walter de Gruyter |isbn=9783110849349 }}
* {{cite book | last=Watkins | first=Calvert | author-link=Calvert Watkins | title=The American Heritage Dictionary of Indo-European Roots | edition=2nd | year=2000 | publisher=Houghton Mifflin | location=Boston & New York | isbn=0-618-08250-6}}

{{Proto-Indo-European language}}

{{DEFAULTSORT:Indo-European Ablaut}}
[[Category:Germanic languages]]
[[Category:Historical linguistics]]
[[Category:Proto-Indo-European language|Ablaut]]
[[Category:Linguistic morphology]]