Indo-European ablaut

Indo-European ablaut is a patterned alternation among vowel grades within related word forms, inherited from Proto-Indo-European and preserved in several descendant languages.

E-grade: The ablaut grade containing the vowel *e in reconstructed Proto-Indo-European forms. It is the full-grade counterpart to the other principal ablaut patterns.
Proto-Indo-European: The reconstructed common ancestor of the Indo-European language family. Ablaut is reconstructed as part of this ancestor’s morphology and phonology.
Strong verb: A Germanic verb that forms its principal past tense by changing its stem vowel. Germanic strong verbs preserve ablaut in a conspicuous inflectional pattern.
Umlaut: A sound change in which a vowel is fronted or otherwise altered under the influence of a following vowel or glide. Unlike inherited ablaut alternations, umlaut arose through conditioned sound change in Germanic.
Franz Bopp: A German linguist whose comparative work helped establish Indo-European historical linguistics in the nineteenth century. His comparisons of inflectional forms helped bring inherited vowel alternations into focus.
O-grade: The ablaut grade containing the vowel *o in reconstructed Proto-Indo-European forms. Its alternation with *e-grade is among the system’s central patterns.
Comparative method: A method for reconstructing ancestral languages by comparing systematic correspondences among related languages. Regular correspondences across branches provide evidence for inherited ablaut patterns.
Germanic languages: A branch of Indo-European that includes English, German, Dutch, and the Scandinavian languages. Their strong-verb classes retain inherited vowel alternations, though reshaped over time.
Apophony: A morphological alternation in a word’s root or affix, often involving a change in vowel quality or quantity. The term names the broader morphological pattern of which Indo-European ablaut is a historical type.
August Schleicher: A nineteenth-century German linguist known for influential work on Indo-European reconstruction and language classification. His comparative reconstructions helped systematize the study of Indo-European morphology.

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