Stemchanging

Stemchanging, or stem-changing, is a phonological process in which the stem of a word alters its vowel or vowel quality when the word is inflected. The change typically targets the stem rather than the affixes and is most common in verbs, though some languages also show stem alternations in adjectives or nouns. Stem changes encode grammatical information such as tense, mood, person, or number while preserving the overall word form.

In Spanish and other Romance languages, many present-tense verbs change the stem vowel in certain forms. Typical patterns include e changing to ie (pensar → pienso, piensas, piensa) and o changing to ue (poder → puedo, puedes, puede). Some -ir verbs also change e to i (pedir → pido, pides, pide). In many cases, the stem change affects all forms except nosotros and vosotros, giving rise to the category of “shoe verbs.”

In German, stem-changing is often described as ablaut in strong verbs, where the stem vowel shifts across tenses. Examples include fahren (present er fährt, past fuhr, past participle gefahren) and lesen (er liest, las, gelesen). These changes are part of verb class systems and influence past tenses and participles rather than noun inflection.

In English, stem-changing appears primarily in irregular or strong verbs with vowel alternations between base, past, and past participle forms (for example, sing–sang–sung; ring–rang–rung; go–went–gone). These patterns are historical remnants of Proto-Germanic ablaut and persist as irregular forms in modern usage.

See also: ablaut, irregular verb, strong verb, shoe verbs.