Editing Indo-European ablaut (section)

==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
| *ph<sub>2</sub>-'''tér'''-m̥
| {{nowrap|{{lang|grc|πα-'''τέρ'''-α}}}}
| pa-'''tér'''-a
| "father"<br/>(noun, accusative)
|-
| lengthened<br/>e-grade
| *ph<sub>2</sub>-'''tḗr'''
| {{nowrap|{{lang|grc|πα-'''τήρ'''}}}}
| pa-'''tḗr'''
| "father"<br/>(noun, nominative)
|-
| zero-grade
| *ph<sub>2</sub>-'''tr'''-és
| {{nowrap|{{lang|grc|πα-'''τρ'''-ός}}}}
| pa-'''tr'''-ós
| "father's"<br/>(noun, genitive)
|-
| o-grade
| *n̥-péh<sub>2</sub>-'''tor'''-m̥
| {{nowrap|{{lang|grc|ἀ-πά-'''τορ'''-α}}}}
| a-pá-'''tor'''-a
| "fatherless"<br/>(adjective, accusative)
|-
| lengthened<br/>o-grade
| *n̥-péh<sub>2</sub>-'''tōr'''
| {{nowrap|{{lang|grc|ἀ-πά-'''τωρ'''}}}}
| 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: ''*deywós'' and its nominative plural ''*deywóes'' show pretonic and posttonic e-grade, respectively, and  ''*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 *ph<sub>2</sub>-tér-s and *n̥-péh<sub>2</sub>-tor-s, changing them to *ph<sub>2</sub>-tḗr and *n̥-péh<sub>2</sub>-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 ''*mḗh₁-n̥s'' "moon", genitive ''*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 *ph<sub>2</sub>trés, which may already have been pronounced something like {{IPA|[pɐtrés]}}, it is not difficult to imagine it as a contraction of an older *ph<sub>2</sub>terés, 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]]). 
*The laryngeals could be pronounced as consonants, in which case they were probably variations on the ''h'' sound and so normally transcribed as h<sub>1</sub>, h<sub>2</sub> and h<sub>3</sub>. However, they could also carry a syllable stress, in which case they were more like vowels. Thus, some linguists prefer to transcribe them ə<sub>1</sub>, ə<sub>2</sub> and ə<sub>3</sub>. 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, ''*bʰergʰ-'') could become CrC (''*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: ''*deywó-'', nominative plural ''*-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 h<sub>2</sub> 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.