In linguistics, the grammatical number of a noun, verb, pronoun or other part of speech, communicates some information about quantity without using numerals. In Modern English there are two states for grammatical numbers: singular (one) and plural (two or more). (Other languages may have more than two values. For example, Old English had three possible forms: singular for one, dual for two and plural for more than two.) Compare the words 'foot' and 'feet'. The first word 'foot' is singular (one), the second is plural (two or more). Some general quantity information has been expressed while using only one word. In a verb, the classification of a word form by grammatical number is know as the case of the verb. For example, the verb 'to be' has the singular case 'is' and plural case 'are'.
Subject noun and verb number agreement
In Modern English, the grammatical number of the subject noun or pronoun in a sentence clause must match the number of the verb. This is known as noun, verb number agreement. To take an example, look at two forms of a noun, boy and boys and how the grammatical number affects the case of the verb associated with them. The word boy is a singular noun whereas boys is a plural form. Now look at a verb such as to be. There are singular forms of the verb such as was, am and is, as well as plural forms were and are; this is called a linguistic paradigm. If we create a simple sentence, then the verb's grammatical number must agree the grammatical number of the subject noun. For example: "The boy is tall." and, "The boys are tall." are correct as the grammatical number of the verb matches that of the subject noun. In contrast: "The boy are tall." and, "The boys is tall." are incorrect as the grammatical number of the subject nouns and verbs are not in agreement. An exception to the rule can sometimes be found in informal British English when referring to singular collective nouns of people. For example, "The government are meeting" would be informally acceptable, whereas the expression "The government is meeting" belongs to the more formal register.