Irregular verb

A regular verb is any verb whose conjugation follows the typical pattern, or one of the typical patterns, of the language to which it belongs. A verb whose conjugation follows a different pattern is called an irregular verb. (This is one instance of the distinction between regular and irregular inflection, which can also apply to other word classes, such as nouns and adjectives.)

In English, for example, verbs such as play, enter, and like are regular, since they form their inflected parts by adding the typical endings -s, -ing and -ed, to give forms such as plays, entering, and liked. On the other hand, verbs such as drink, hit and have are irregular, since some of their parts are not made according to the typical pattern – drank and drunk (not "drinked"); hit (as past tense and past participle, not "hitted") and has and had (not "haves" and "haved").

The classification of verbs as regular or irregular is to some extent a subjective matter. If some conjugational paradigm in a language is followed by a limited number of verbs, or requires the specification of more than one principal part (as with the German strong verbs), views may differ as to whether the verbs in question should be considered irregular. Most inflectional irregularities arise as a result of series of fairly uniform historical changes, so forms that appear to be irregular from a synchronic (contemporary) point of view may be seen as following more regular patterns when analyzed from a diachronic (historical linguistic) viewpoint.

When a language develops some type of inflection, such as verb conjugation, it normally produces certain typical (regular) patterns by which words in the given class come to make their inflected forms. The language may develop a number of different regular patterns, either as a result of conditional sound changes which cause differentiation within a single pattern, or through patterns with different derivations coming to be used for the same purpose. An example of the latter is provided by the strong and weak verbs of the Germanic languages; the strong verbs inherited their method of making past forms (vowel ablaut) from Proto-Indo-European, while for the weak verbs a different method (addition of dental suffixes) developed.

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