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The 11 pages that link to Grammatical number, each with the reason it gives.
InflectionRelated: Number is commonly expressed through inflection on nouns, pronouns, and verbs.
Grammatical genderRelated: Number frequently combines with gender in agreement patterns.
Person (grammar)Related: Person and number commonly combine in pronoun forms and verb paradigms.
DeclensionRelated: Declined forms often distinguish singular from plural.