Irregularity and Suppletion
An irregular paradigm is one in which the derived forms of a word cannot be deduced by simple rules from the base form. For example, someone who knows only a little English can deduce that the plural of girl is girls but cannot deduce that the plural of man is men. Language learners are often most aware of irregular verbs, but any part of speech with inflections can be irregular. For most synchronic purposes — first language acquisition studies, psycholinguistics, language teaching theory — it is enough to note that these forms are irregular. However historical linguistics seeks to explain how they came to be so and distinguishes different kinds of irregularity according to their origins. Most irregular paradigms (like man:men) can be explained by philological developments that affected one form of a word but not another. The historical antecedents of the current forms were once a regular paradigm. The term "suppletion" was coined by historical linguists to distinguish irregularities like person:people that cannot be so explained, because the parts of the paradigm have not evolved out of a single form.
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