Parts of speech

Parts of speech are types of word in grammar. There are many different word categories: they are called 'lexical categories'. The most common are these:

Part of Speech	Function	Example Words	Example Sentence(s)	Notes
Verb	Identifies an action or state.	(to) be, have, do, like, work, sing, can, must	London is a big city. I like London.	A verb has a subject, which is a noun performing the action. Some verbs also have an object, which receives the action.
Noun	Identifies a person, place or thing.	pen, dog, work, music, town, London, teacher, John	New York City is very beautiful.	Proper nouns are a type of noun that refers to something individual. Two proper nouns are New York City and the name Amelia. Proper nouns are capitalized. Other nouns are called common nouns.
Adjective	Describes a noun.	good, big, red, interesting	The cat is black and white.
Adverb	Describes a verb, adjective or adverb.	quickly, silently, well, badly, very, really	The giraffe eats slowly, but when he is very hungry, he eats really quickly.	Slowly describes the verb eat, very describes the adjective hungry and really describes the adverb quickly.
Pronoun	Replaces a noun.	I, you, he, she, some, it	She is very good at playing the piano.
Preposition	Links a noun to another word.	to, at, after, on, under	The dog is under the table. The man ran over the bridge.	Under links the noun dog to the noun table. Over links the verb ran to the noun bridge.
Conjunction	Joins clauses, sentences or words.	and, but, when, or	I like apples and oranges, but I don't like grapes.
Determiner	Helps refer to a noun.	the, a, an, my, your,this, that	There is a drink on the table. It is my drink.
Interjection	Short exclamation.	oh!, ouch!, hi!	Ouch! That really hurt!

Open and closed classes

Verbs, nouns, adjectives, adverbs, and interjections are called open classes because they are parts of speech that can easily add new words. On the other hand, pronouns, prepositions, and conjunctions are closed classes because new words cannot be added easily. For example, since pronouns are a closed class, there are fairly few pronouns: I, me, my, mine, myself, you, your, yours, yourself, he, him, his, his, himself, she, her, her, hers, herself, it, it, its, its, itself, we, us, our, ours, ourselves, they, them, their, theirs, themselves. Since pronouns are used to replace whole noun phrases, there is no need to have many kinds of pronouns. Instead of saying "The Earl of Sandwich introduced the Earl of Sandwich's favorite food, the sandwich", one uses the pronoun his to replace "the Earl of Sandwich's" to make the sentence not repeat itself when it doesn't have to, thus the sentence becomes "The Earl of Sandwich introduced his favorite food, the sandwich". New nouns, on the other hand, can easily be made, and are constantly being added into the English language.