Indo-European ablautIn linguistics, the Indo-European ablaut (ˈæblaʊt, from German Ablaut ˈaplaʊt) is a system of apophony (regular vowel variations) in the Proto-Indo-European language (PIE). An example of ablaut in English is the strong verb sing, sang, sung and its related noun song, a paradigm inherited directly from the Proto-Indo-European stage of the language. Traces of ablaut are found in all modern Indo-European languages, though its prevalence varies greatly.
ApophonyIn linguistics, apophony (also known as ablaut, (vowel) gradation, (vowel) mutation, alternation, internal modification, stem modification, stem alternation, replacive morphology, stem mutation, internal inflection etc.) is any alternation within a word that indicates grammatical information (often inflectional). Apophony is exemplified in English as the internal vowel alternations that produce such related words as sng, sng, sng, sng bnd, bnd bld, bld brd, brd dm, dm fd, fd l, l rse, rse, rsen wve, wve ft, ft gse, gse tth, tth The difference in these vowels marks variously a difference in tense or aspect (e.