[[PIE phonology MOC]]
# Ablaut
Everyone's favourite [[apophony]], already lying on the boundary between phonology and [[PIE morphology MOC|morphology]] in PIE.

-   <em class="recon">ē</em> ~ <em class="recon">e</em> ~ ∅ ~ <em class="recon">o</em> ~ <em class="recon">ō</em>
-   <em class="recon">ā</em> ~ <em class="recon">a</em> ~ ∅

## Overview

- **o-grade rule** 
  - Underlying <em class="recon">e</em> or ∅ are changed to the o-grade in a disjunct set of morphological environments (==[[PIE strong cases]]==, ==sg. active indicative==).
  - It would also seem that <em class="recon">o</em> replaces ∅ where the latter would be otherwise inadmissible,
    e.g. acc. sg. <em class="recon">swésor-ṃ</em> ‘sister’,
    though the reason is not clear here.
  - Similarly pretonic root syllables for derived causative verbs take the o-grade,
    e.g. 3sg. <em class="recon">woséyeti</em> ‘clothes sb‘.[^201714] <!--SR:!2023-11-10,13,210!2023-12-14,55,250-->

- **∅-grade rule**
  Surface unaccented ablauting vowels would often be deleted,
  especially in stems but also in derivations. Exceptions are numerous:
  - Unaccented ablauting vowels are visible in <em class="recon">pédes</em> ‘of a foot’ (cf. Latin <em class="ling">pedis</em>)
  and <em class="recon">nébʰesos</em> ‘of a cloud’ (cf. Homeric Greek <em class="ling">νέφεος</em>);
  - Accented ∅ can likewise be found in <em class="recon">wḷ́kʷos</em> ‘wolf’ and <em class="recon">h₂ṛ́tkos</em> ‘bear’.
  So the rule is already partially morphologised in PIE.
  [^201714]
- **lengthened grade rule** Some nominals exhibit a lengthened grade in the [[PIE strong cases|strong cases]], and verbs in the indicative singular active.
  See also [[PIE vowel lengthening by contraction]].<!--SR:!2023-09-11,41,250!2023-12-09,90,230-->

[^201714]: 2017\. [[Sources/@ringeProtoIndoEuropeanProtoGermanic2017|From Proto-Indo-European to Proto-Germanic]], p. 14


The [[PIE thematic vowel]] followed a special version of the o-grade and ∅-grade rules, listed in that note.

## In daughter languages
In part due to [[PIE *e-laryngeal colouring]] and the [[PIE Laryngeal Theory|loss of laryngeals]] in most daughter languages,
the ablaut system had to be reinterpreted in all daughter languages.

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