Stemalternants

Stemalternants, or stem alternants, are alternate forms of the stem of a word that occur in different grammatical forms. This phenomenon is most common in the inflection of verbs in Germanic languages, where the root vowel (and sometimes the root consonant) changes across tenses, aspects, numbers, or participles. The alternations are often described in terms of ablaut (internal vowel changes) and, in some cases, umlaut (vowel modification caused by a suffix).

In English, classic examples are the strong verbs, such as sing-sang-sung, swim-swam-swum, and ring-rang-rung, where the stem vowel shifts with each past tense or participle form. German and Dutch demonstrate similar patterns: fahren-fährt-fuhr-gefahren and laufen-läuft-lief-gelaufen in German, or lopen-loopt-liep-gelopen in Dutch, show how the stem reorganizes to signal grammatical information. These alternants provide a compact way to encode tense, aspect, or voice within a single lexical item.

Typologically, stemalternants are a key feature of ablaut-driven morphology, especially in Proto-Indo-European derivatives, and they survive today as irregular or strong-verb paradigms in several languages. In many modern varieties, productive alternation has diminished, giving way to periphrastic or analytically formed tenses, while a subset of stemalternants remains as irregular lexemes or fossilized patterns.

See also: ablaut, umlaut, irregular verbs.