English grammar is the body of rules that describe the structure of expressions in the English language. This includes the structure of words, phrases, clauses, and sentences. There are historical, social, and regional variations of English. Divergences from the grammar described here occur in some dialects of English. This article describes a generalized present-day Standard English, the form of speech found in types of public discourse including broadcasting, education, entertainment, government, and news reporting, including both formal and informal speech. There are certain differences in grammar between the standard forms of British English, American English, and Australian English, although these are inconspicuous compared with the lexical and pronunciation differences.

There are eight word classes, or parts of speech, that are distinguished in English: nouns, determiners, pronouns, verbs, adjectives, adverbs, prepositions, and conjunctions. (Determiners, traditionally classified along with adjectives, have not always been regarded as a separate part of speech.) Interjections are another word class, but these are not described here as they do not form part of the clause and sentence structure of the language. Nouns, verbs, adjectives, and adverbs form open classes – word classes that readily accept new members, such as the noun celebutante (a celebrity who frequents the fashion circles), the adverb 24/7 (as in I am working on it 24/7), and similar relatively new words. The others are regarded as closed classes. For example, it is rare for a new pronoun to be admitted to the language. English words are not generally marked for word class. It is not usually possible to tell from the form of a word which class it belongs to except, to some extent, in the case of words with inflectional endings or derivational suffixes. On the other hand, some words belong to more than one word class. For example run can serve as either a verb or a noun (these are regarded as two different lexemes). Lexemes may be inflected to express different grammatical categories. The lexeme run has the forms runs, ran, and running. Words in one class can sometimes be derived from those in another. This has the potential to give rise to new words. The noun aerobics has recently given rise to the adjective aerobicized. Wordsses. A phrase typically serves the same function as a word from some particular word class. For example, my very good friend Peter is a phrase that can be used in a sentence as if it were a noun, and is therefore called a noun phrase. Similarly, adjective phrases and adverb phrases function as if they were adjectives or adverbs, but with other types of phrases the terminology has different implications. For example, a verb phrase consists of a verb together with any objects and other dependents; a prepositional phrase consists of a preposition together with its complement (and is therefore usually a type of adverb phrase); and a determiner phrase is a type of noun phrase containing a determiner.