The category of number is proper to count nouns only. Usually words which lack a certain category, have only one form, that of the weak member of the opposition. Non-counts may be singular or plural. So subclasses of non-count nouns constitute a lexico-grammatical opposition “singular only - plural only”: snow, joy, news - contents, tongs, police.
The general meaning revealed through the grammatical opposition a book - books is number, or quantity, or “oneness - more than-oneness”. The general meaning revealed througli the lexico-grammatical opposition is “discreteness - non-discreteness”. The opposition “discreteness - non-discreteness” is semantically broader than the opposition “oneness - more-than-oneness”. It embraces both countable and uncountable nouns. Singular presents the noun-referent as a single indiscrete entity. Plural presents the referent as a multiplicity of discrete entities (separate objects - houses; objects consisting of separate parts - scissors; various types - wines, etc.).