Суплетивизм в языке: нерегулярные формы и разные основы слов

A word having inflected forms from multiple unrelated stems
In linguistics and etymology, suppletion is traditionally understood as the use of one word as the inflected form of another word when the two words are not cognate. For those learning a language, suppletive forms will be seen as "irregular" or even "highly irregular". The term "suppletion" implies that a gap in the paradigm was filled by a form "supplied" by a different paradigm. Instances of suppletion are overwhelmingly restricted to the most commonly used lexical items in a language.

The Romanian verb a fi ("to be") is suppletive and irregular, with the infinitive coming from Latin fieri, but conjugated forms from forms of already suppletive Latin sum. For example, eu sunt ("I am"), tu ești ("you are"), eu am fost ("I have been"), eu eram ("I used to be"), eu fusei/fui ("I was"); while the subjunctive, also used to form the future in o să fiu ("I will be/am going to be"), is linked to the infinitive.

In Russian, the word человек ("man, human being") is suppletive. The strict plural form, человеки, is used only in Orthodox Church contexts, with numerals (e. g. пять человек "five people") and in humorous context. It may have originally been the unattested человекы. In any case, in modern usage, it has been replaced by люди, the singular form of which is known in Russian only as a component of compound words (such as простолюдин). This suppletion also exists in Polish (człowiek > ludzie), Czech (člověk > lidé), Serbo Croatian (čovjek > ljudi), Slovene (človek > ljudje), and Macedonian (човек (chovek) > луѓе (lugje)).

Strictly speaking, suppletion occurs when different inflections of a lexeme (i. e., with the same lexical category) have etymologically unrelated stems. The term is also used in looser senses, albeit less formally.

The term "suppletion" is also used in the looser sense when there is a semantic link between words but not an etymological one; unlike the strict inflectional sense, these may be in different lexical categories, such as noun/verb. English noun/adjective pairs such as father/paternal or cow/bovine are also referred to as collateral adjectives. In this sense of the term, father/fatherly is non suppletive. Fatherly is derived from father, while father/paternal is suppletive. Likewise cow/cowish is non suppletive, while cow/bovine is suppletive. In these cases, father/pater and cow/bov are cognate via Proto Indo European, but 'paternal' and 'bovine' are borrowings into English (via Old French and Latin). The pairs are distantly etymologically related, but the words are not from a single Modern English stem.

The term "weak suppletion" is sometimes used in contemporary synchronic morphology in reference to sets of stems whose alternations cannot be accounted for by synchronically productive phonological rules. For example, the two forms child/children are etymologically from the same source, but the alternation does not reflect any regular morphological process in modern English: this makes the pair appear to be suppletive, even though the forms go back to the same root. In that understanding, English has abundant examples of weak suppletion in its verbal inflection: e. g. bring/brought, take/took, see/saw, etc. Even though the forms are etymologically related in each pair, no productive morphological rule can derive one form from the other in synchrony. Alternations just have to be learned by speakers — in much the same way as truly suppletive pairs such as go/went. Such cases, which were traditionally simply labelled "irregular", are sometimes described with the term "weak suppletion", so as to restrict the term "suppletion" to etymologically unrelated stems.