 Supletion is the replacement of one stem with another, resulting in an alimorph of a morpheme which has no phonological similarity to the other alimorphs. Supletion occurs when the syntax requires a form of a lexeme that is not morphologically predictable. Standard illustrations of supletion in English include the forms of the verb B, the degrees of comparison of some adjectives, and the non-derived forms of ordinal numbers. Defining supletion is more complicated than it may seem. Permanent issues concern long-debated theoretical notions such as word, morpheme, regularity, productivity, and the dichotomy between derivation and inflection. For a long time, the database on supletion was restricted to Indo-European languages. However, large-scale cross-linguistic studies have observed the phenomenon in many languages around the globe. Different kinds of supletion affect different linguistic signs – stem supletion and affix supletion. Thus, it is customary to distinguish between affixel and stem supletion. An English example of affixel supletion is the plural affix En as in oxen. It is not motivated by any morphophonological rules of English, unlike other plural alimorphs such as boys and cups.