Definition · Plain-language
Parts of speech
The parts of speech are the categories into which words are sorted by their job in a sentence — traditionally eight: noun, pronoun, verb, adverb, adjective, preposition, conjunction and interjection.
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The eight traditional classes
Every word in English belongs to at least one part of speech — a class defined by the grammatical job the word does. The traditional eight are: nouns, which name people, places, things and ideas (teacher, London, freedom); pronouns, which stand in for nouns (she, it, they); verbs, which express action or state (run, is); adjectives, which describe nouns (tall, blue); adverbs, which modify verbs, adjectives and other adverbs (quickly, very); prepositions, which show relationships of time, place and direction (in, on, by); conjunctions, which join words and clauses (and, but, because); and interjections, which express sudden emotion (wow, ouch). Together they account for how words combine into meaningful sentences.
Determiners and the ninth class
Many modern grammars recognise a ninth part of speech: the determiner, sometimes treated more narrowly as the article. Determiners are words that introduce and specify nouns — the articles a, an and the, plus words like this, that, my, some and every. Traditional grammar often folded these in with adjectives, since both sit before nouns, but they behave differently: a determiner identifies or quantifies a noun rather than describing its qualities. Whether you count eight classes or nine is largely a matter of which grammar you follow; the important point is that determiners do a distinct job from the descriptive adjectives they are sometimes grouped with.
Why the same word can change class
A crucial idea is that part of speech is about a word’s function in a particular sentence, not a fixed label the word carries everywhere. Many English words shift class depending on use. "Book" is a noun in "I read a book" but a verb in "I will book a table". "Fast" is an adjective in "a fast car", an adverb in "she runs fast" and even a verb in "they fast during the day". This is why you cannot always tell a word’s part of speech in isolation; you have to see how it works in the sentence. Identifying parts of speech accurately is the foundation for understanding grammar, punctuation and sentence structure.
Key facts
At a glance
- Definition: the categories that classify words by their job in a sentence
- The eight: noun, pronoun, verb, adjective, adverb, preposition, conjunction, interjection
- Possible ninth: the determiner or article (a, the, this, my)
- Open classes: nouns, verbs, adjectives, adverbs (gain new words)
- Closed classes: pronouns, prepositions, conjunctions (rarely add members)
- Key idea: a word’s class depends on its function in the sentence
Common misconceptions
What people often get wrong
Often heard: There are exactly eight parts of speech, no more and no less.
Actually: Eight is the traditional count, but many modern grammars add a ninth, the determiner or article (a, the, this). The number depends on which grammatical framework you follow.
Often heard: Each word belongs to one fixed part of speech for ever.
Actually: A word’s part of speech depends on its function in a sentence. "Book" is a noun in "a book" but a verb in "to book a table"; many words change class with use.
Often heard: Determiners like "the" and "my" are just adjectives.
Actually: Determiners do a distinct job: they introduce and specify a noun rather than describe its qualities. Many grammars treat them as a separate class from descriptive adjectives.
Going deeper
