A part of speech is a term used in traditional grammar for one of the nine main categories into which words are classified according to their functions in sentences, such as nouns or verbs. Also known as word classes, these are the building blocks ofgrammar.
Every sentence you write or speak in English includes words that fall into some of the nine parts of speech. These include nouns, pronouns, verbs, adjectives, adverbs, prepositions, conjunctions, articles/determiners, and interjections. (Some sources include only eight parts of speech and leave interjections in their own category.)
Learning the names of the parts of speech probably won’t make you witty, healthy, wealthy, or wise. In fact, learning just the names of the parts of speech won’t even make you a better writer. However, you will gain a basic understanding of sentence structure and the English language by familiarizing yourself with these labels.
Open and Closed Word Classes
The parts of speech are commonly divided into open classes (nouns, verbs, adjectives, and adverbs) and closed classes (pronouns, prepositions, conjunctions, articles/determiners, and interjections). The idea is that open classes can be altered and added to as language develops and closed classes are pretty much set in stone. For example, new nouns are created every day, but conjunctions never change.
In contemporary linguistics, the label part of speech has generally been discarded in favor of the term word class or syntactic category. These terms make words easier to qualify objectively based on word construction rather than context. Within word classes, there is the lexical or open class and the function or closed class.
The 9 Parts of Speech
Noun
Nouns are a person, place, thing, or idea. They can take on a myriad of roles in a sentence, from the subject of it all to the object of an action. They are capitalized when they’re the official name of something or someone, called proper nouns in these cases. Examples: pirate, Caribbean, ship, freedom, Captain Jack Sparrow.
Pronoun
Pronouns stand in for nouns in a sentence. They are more generic versions of nouns that refer only to people. Examples: I, you, he, she, it, ours, them, who, which, anybody, ourselves.
Verb
Verbs are action words that tell what happens in a sentence. They can also show a sentence subject’s state of being (is, was). Verbs change form based on tense (present, past) and count distinction (singular or plural). Examples: sing, dance, believes, seemed, finish, eat, drink, be, became
Adjective
Adjectives describe nouns and pronouns. They specify which one, how much, what kind, and more. Adjectives allow readers and listeners to use their senses to imagine something more clearly. Examples: hot, lazy, funny, unique, bright, beautiful, poor, smooth.
Adverb
Adverbs describe verbs, adjectives, and even other adverbs. They specify when, where, how, and why something happened and to what extent or how often. Examples: softly, lazily, often, only, hopefully, softly, sometimes.
Preposition
Prepositions show spacial, temporal, and role relations between a noun or pronoun and the other words in a sentence. They come at the start of a prepositional phrase, which contains a preposition and its object. Examples: up, over, against, by, for, into, close to, out of, apart from.
Conjunction
Conjunctions join words, phrases, and clauses in a sentence. There are coordinating, subordinating, and correlative conjunctions. Examples: and, but, or, so, yet, with.
Articles and Determiners
Articles and determiners function like adjectives by modifying nouns, but they are different than adjectives in that they are necessary for a sentence to have proper syntax. Articles and determiners specify and identify nouns, and there are indefinite and definite articles. Examples: articles: a, an, the; determiners: these, that, those, enough, much, few, which, what.
Some traditional grammars have treated articles as a distinct part of speech. Modern grammars, however, more often include articles in the category of determiners, which identify or quantify a noun. Even though they modify nouns like adjectives, articles are different in that they are essential to the proper syntax of a sentence, just as determiners are necessary to convey the meaning of a sentence, while adjectives are optional.
Interjection
Interjections are expressions that can stand on their own or be contained within sentences. These words and phrases often carry strong emotions and convey reactions. Examples: ah, whoops, ouch, yabba dabba do!
Source: https://www.thoughtco.com/part-of-speech-english-grammar-1691590 and written by Richard Nordquist
