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University of Michigan - Ann Arbor

While word classes do have semantic tendencies—adjectives, for example, often describe properties and nouns people— parts of speech are defined instead based on their grammatical relationship with neighboring words or the morphological properties about their affixes.

English Word Classes

An on-going but a helpful book resource about NLP
https://web.stanford.edu/~jurafsky/slp3/

Speech and Language Processing (3rd ed. draft) 

Closed classes are those with relatively fixed membership, such as prepositions— new prepositions are rarely coined. Closed class words are generally function words like of, it, and, or you, which tend to be very short, occur frequently, and often have structuring uses in grammar.

Closed class

Open classes are changed frequently —  new words like iPhone or to fax are continually being created or borrowed. Four major open classes occur in the languages of the world: nouns (including proper nouns), verbs, adjectives, and adverbs, as well as the smaller open class of interjections.

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