Words have different uses in sentences. According to their uses, words are divided into classes called Parts of Speech.
The parts of speech are as follows:
1. NOUN - a word used as the name of something. Ex: man, box, Pittsburgh, Harry, silence, justice.
2. PRONOUN - a word used instead of a noun. Ex: I, he, it, that.
Nouns, pronouns, or groups of words that are used as nouns or pronouns, are called by the general term - SUBSTANTIVES.
3. ADJECTIVE - a word used to limit or qualify the meaning of a noun or a pronoun. Ex: good, five, tall, many.
A, an, and the are words used to modify nouns or pronouns. They are adjectives, but are usually called ARTICLES.
4. VERB - a word used to state something about some person or thing. Ex: do, see, think, make.
5. ADVERB - a word used to modify the meaning of a verb, an adjective, or another adverb. Ex: very, slowly, clearly, often.
6. PREPOSITION - a word used to join a substantive, as a modifier, to some other preceding word, and to show the relation of the substantive to that word. Ex: by, in, between, beyond.
7. CONJUNCTION - a word used to connect words, phrases, clauses, and sentences. Ex: and, but, if, although, or.
8. INTERJECTION - a word used to express surprise or emotion. Ex: Oh! Alas! Hurrah! Bah!
Sometimes a word adds nothing to the meaning of the sentence, but helps to fill out its form or sound, and serves as a device to alter its natural order. Such a word is called an EXPLETIVE. In the following sentence there is an expletive: There are no such books in print.