1. The category of the Number is based on the opposition of singularity and plurality.
For example:
parent – parents, tree –trees, man –men, life – lives, etc.
Singular form of the Noun is multiciphered (ìíîãîçíà÷íîå; can stay singular or change into plural) and Plural – simple (îäíîçíà÷íîå; cannot change for has already been changed).
The opposition of singularity and plurality can, for example:
1) express differences in size (ex., wood (like material to be used to make a fire; logs) and woods (like an area of trees, smaller than a forest));
2) distinguish a class and a subclass (ex., fish (as a creature that lives in water) and fishes (refers to different kinds of fish)).
2. The category of the Number as for the formal indices is presented in two general models – open and closed.
1). As for the open model or productive (it goes on working) it is displayed by the formal index – the suffix -s/-es (in the Plural form of the Noun) or by its absence (in the Singular one).
For example:
Star – stars, floor –floors, knife – knives, etc.
*To the allomorphemes of the suffix -s/-es the following three are included:
1) [s]; after voiceless (unvoiced, surd, breathed) consonants (ex., cats);
2) [z] after vowels (ex., indices) and voiced consonants (ex., dogs);
3) [iz] sibilant (ex., kisses) and hushing sounds (ex., bushes).
2). As for the closed model (it is a certain historical heritage and does not develop) it is grammatically displayed only morphologically or in the sequence with a verb:
1) morphologically: Ox – oxen, child – children, woman –women, man – men, phenomenon – phenomena, antenna – antennae, data – datum, etc.
2) in the sequence with a verb: the noun sheep does not change its grammatical form at all: The sheep is here (Singular Number). The sheep are here (Plural Number).
3). There are also nouns which are unchangeable and have only singular or only plural form:
a) only singular: advice, information, knowledge, furniture, etc.;
b) only plural: trousers, pants, pyjamas, spectacles, etc.