Open and Closed Word Classes
How do I know if a word is open or closed class? To answer that question, consider this analogy. A construction crew is building a high-rise. They create the foundation, establish a steel framework, and then make sure electricity and water is available. Those elements are all closed class. The construction crew then creates floors and walls, as well as the rest of the decor. Those are like open class categories.
What does that mean? Well, like the steel skeleton of a building, closed class words are highly functional and serve to connect and support other elements. Closed class words are sometimes also called function or grammatical words. They include the following categories: determiners, pronouns, prepositions and conjunctions. Open class words are analogous to the walls, windows, décor and external architecture of a building because they are rich in meaning and are frequently modified. Contrary to function words, open class words contain a lot of semantic content. They are often called lexical or content words and include the following categories: nouns, verbs, adjectives and adverbs.
Another way to distinguish between open and closed class is to think about the possibility of adding a word to a given category. Is it possible to create new nouns? Sure, it happens every day. It is clear that all nouns are open class words. Consider whether it is likely that new articles or conjunctions will be added to English soon. It is highly unlikely, which is one reason why those categories are closed class.
