The attraction of umlaut by -er is highlighted by the existence of a handful of plural doublets, where nouns, one in -e, and one in -er have different plurals with slightly different semantic/pragmatic connotations (5). Strikingly these words don’t show umlaut if they form the plural in...
In the case of déranger, the verb stem is dérang- and the first person plural ending is -ons. Since both the 'a' in dérang- and the 'o' in -ons are vowel sounds, an 'e' is added between them to make the pronunciation smoother. This results in the conjugated form nous dérange...
These alternations contrast with near-minimal pairs of nouns and adjectives that keep the same form in the singular and in the plural, as in (2). In addition, some variable nouns and adjectives can take either kind of plural, e.g. [val] ‘valley’, [beʁkaj] ‘home’. The alternati...