alternation: the situation in which there are changes in linguistic forms (especially phonological forms of morphemes) which do not affect meaning. For example, the prefix "in-" 'negative' in English (inadmissible, intolerant) can also appear as "im-" (impossible), "ir-" (irrelevant) and "il-" (illegal). In all these cases the meaning 'negative' is the same, so this is a case of alternation. The different forms are called allomorphs of the prefix. Alternations can be morphophonemic (when the segments which alternate belong to different phonemes) or allophonic (when the segments which alternate belong to the same phoneme); in both cases they provide important evidence for phonological analysis. There can also be alternations of forms that are phonologically unrelated; these are termed suppletive. Alternation is often represented with a tilde [2] (~): "in- ~ im- ~ ir- ~ il-"; sometimes a slash [2] (/) is used instead: "in-/im-/ir-/il-". [Spanish: alternancia]