By studying the following nouns and pronouns we see that different meanings are shown by the different forms of the same words: boy, boys; box, boxes; tree, trees; chair, chairs; fox, foxes; man, men; child, children; I, we; he, they.
By using the words boy, box, tree, etc., we think of one of each kind of the objects mentioned. When the words boys, boxes, trees, etc., are used we think of more than one of each kind of object mentioned.
When a single object of a kind is denoted by a word, the word is said to be in the singular number.
When more than one object of a kind is denoted by a word, the word is said to be in the plural number.
Number is the form of the noun or pronoun which denotes one object or more than one.
Nouns have two numbers, the singular and the plural.
The singular number of a noun or pronoun is its form to denote one object.
The plural number of a noun or pronoun is its form to denote more than one object.