Wendy Wilson, James H. Barlow. Advanced English Grammar. , , 2020.

The parts of speech are the categories into which each word in the language fits. In a sentence, each part of speech plays a different purpose, and certain words, depending on their use in a specific sentence, may be more than one part of speech. These parts of speech are the language's building blocks. When individuals refer to the parts of speech, they mean these eight categories that can be placed in all words.