suppletion

Suppletion is a linguistic phenomenon in which an inflected form of a word is formed from a stem that is etymologically unrelated to the stems of the other forms in the same paradigm. In other words, the different morphological forms of a word come from different roots rather than being derived by regular affixation or vowel alternation within a single root. The term, from Latin suppletus meaning “supplied,” was introduced by 19th-century grammarians to describe paradigms that must be supplied from separate roots.

Suppletion is most common in verb inflection. The classic English example is the verb to be: I am, you are, he is, we are, they are; past tense I was, you were, he was, we were, they were. The forms am/is/are and was/were come from historically different roots. Another well-known example is the past tense of go, which is went, derived from a different stem than go. In adjectives, the comparative and superlative of good are better and best, formed from a separate root rather than by regular inflection of good.

Suppletion occurs across many languages and language families, reflecting long-term historical changes, contact, and analogy. It stands apart from irregular phonological alternations because the related forms are typically derived from distinct lexical roots rather than from a single root with irregular affixes.