The parts of speech explain how a word is used in a sentence.There are eight main parts of speech (also known as word classes): nouns, pronouns, adjectives, verbs, adverbs, prepositions, conjunctions, and interjections.Most parts of speech can be divided into sub-classes. Prepositions can be divided into prepositions of time, prepositions of place, etc. Nouns can be divided into proper nouns, common nouns, concrete nouns, etc.