[[PIE morphology MOC]]
# PIE thematic vowel

The **thematic vowel** was an [[Ablaut|ablauting]] suffix <em class="recon">-e/o-</em> that could occur at the end of stems.
It was largely functionless but was part of a large number of suffixes for both [[PIE verb stem formation]] and [[PIE nominal stem formation]].
Perhaps the only time it was meaningful on its own was in the formation of the [[Core IE thematic subjunctive]].

Thematic vowels followed a special version of the usual ablaut rules, namely:[^ablaut]

- ∅-grade only occurs when followed by particular derivational suffixes (such as <em class="recon">-yó-</em>)
- For verbs, e-grade only occurred:
  - word-finally, i.e. active 2sg. imperative, e.g. <em class="recon">wérye</em> ‘say!’
  - in e-grade [[Core IE thematic subjunctive#Double-thematic|Core IE double thematic subjunctive]]
  - before coronal obstruents. e.g. imperative 2sg. <em class="recon">wéryeti</em> ‘you say’
- For nominals, the e-grade only occurred
  - word finally, e.g. voc sg. <em class="recon">swéḱure</em> ‘father-in-law!’
  - before <em class="recon">h₂</em> as <em class="recon">a</em> (by [[PIE *e-laryngeal colouring]]), e.g. neut. collective <em class="recon">werǵáh₂</em> ‘work’

Since <em class="recon">o</em> occurred in all other cases, thematic stems are sometimes called o-stems.

[^ablaut]: 2017\. [[Sources/@ringeProtoIndoEuropeanProtoGermanic2017|From Proto-Indo-European to Proto-Germanic]], p. 14–15

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