Number refers to the singular or plural form. Keep the number of a noun in mind when choosing pronouns, noun endings, articles, and subject-verb agreement endings.
Countable nouns can be either singular or plural. Uncountable nouns can usually appear only in the singular.
When you use a noun in the plural, add the plural ending (usually -s) to the singular of the noun.
Some nouns have irregular plural forms--for example, foot, feet; child, children; and sheep, sheep. If you are unsure of the plural form of a noun, check the noun in a dictionary.
When you use a plural noun as a subject, you must use a plural verb. See Subject-Verb Agreement.
Do not use the indefinite article a or an with plural nouns. See Articles.
When using a pronoun to replace a singular noun that refers to a person whose gender is unknown (for example, scientist, student), be careful to avoid sexist language. Do not replace a singular noun with the plural pronoun they. Usually the best course is one of the following: make the noun (hence the pronoun) plural, use a gender-free paraphrase such as person, or rephrase entirely to avoid mention of gender.
When replacing a plural noun with a pronoun, choose the plural pronoun they.