This article discusses plural marking in French Noun Phrases (NPs), arguing that its grammar in Spoken French (SF) is distinct from that of Written French. Three assumptions are put forward: (i) In SF, number fails to be specified on the head noun; it is morphologically specified on determiners (articles, demonstratives and possessives), and lexically specified on quantifiers and ‘set’ terms. (ii) This state of affairs does not result from a phonological change affecting the /s/ coda. (iii) Errors made by French speakers in their written productions are but clues revealing their SF grammar.