Editing Indo-European ablaut (section)

==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 ''*pértus'', from which the English words ''ford'' and (via Latin) ''port'' are derived (both via the zero-grade stem ''*pr̥t-'').

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

An example in a verb is *bʰeydʰ- "to wait" (cf. "bide").

{| class="wikitable"
|-
|
|
| e-grade
|
|-
| Perfect (third-person singular)
| *bʰe-bʰóydʰ-e
| o-grade
| (note [[reduplication|reduplicating]] prefix)
|-
| Perfect (third plural)
| *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]]
|
|
|-
| ''agō''
| ''ēgī''
| "to do"
|
|-
| ''videō''
| ''vīdī''
| "to see"
| (vowel lengthening)
|-
| ''sedeō''
| ''sēdī''
| "to sit"
| (vowel lengthening)
|-
|}

Ablaut can often explain apparently random irregularities. For example, the verb "to be" in Latin has the forms ''est'' (he is) and ''sunt'' (they are). The equivalent forms in German are very similar: ''ist'' and ''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> ''*estь'' and ''*sǫtь'', and developed into e.g. Polish ''jest'' and ''są''.

The difference between singular and plural in these languages is easily explained: the PIE root is ''*h<sub>1</sub>es-''. In the singular, the stem is stressed, so it remains in the e-grade, and it takes the inflection ''-ti''. In the plural, however, the inflection ''-énti'' was stressed, causing the stem to reduce to the zero grade: ''*h<sub>1</sub>es-énti'' → ''*h<sub>1</sub>s-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 ''gónos'' "offspring", Sanskrit ''jánas'' "creature, person"; Greek ''trókhos'' "circular course" < "*act of running");
# ending-stressed feminine, originally collective, action nouns (Greek ''gonḗ'' "offspring", Sanskrit ''janā́'' "birth");
# ending-stressed masculine agent nouns (Greek ''trokhós'' "wheel" < "*runner").
* Nominative, vocative and accusative singular of certain nouns ([[Proto-Indo-European nominals#Athematic and thematic nominals|acrostatic]] root nouns such as ''dṓm'', plural ''dómes'' "house"; [[Proto-Indo-European nominals#Athematic and thematic nominals|proterokinetic]] neuter nouns such as ''*wódr̥'' "water" or ''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.