A closed class is a linguistic category of words which typically includes those types of words that are relatively set in stone for a language and cannot easily be changed. This class of words can vary quite a bit from one language to another, though in English it typically refers to words such as articles, pronouns, and prepositions. These are in contrast to open classes of words, which can be added to with relative ease and include verbs and nouns in English. A closed class may change and adopt new words over time, but the process is typically much slower than for open classes.
The term “closed class” does not necessarily refer to an absolute category of words, but rather to those categories that remain stable in a particular language. This means that such words are not necessarily categorized as a closed class, but are usually instead categorized by the part of speech to which they belong. Words like “cat,” “building,” “milk,” and “orangutan” are all part of the open class in English, but they are referred to as nouns instead. The closed and open classes of words are usually considered by linguists and grammarians, and are typically not a conscious consideration of those who casually speak a language.
A closed class of words in one language may be different from those closed in another language. In English, for example, the closed class includes prepositions, pronouns, and articles that are commonly used. This means that words such as “the,” “a,” “he,” “they,” “to,” “from,” and “our” are all part of the closed class in English. These are words that remain stable and new pronouns or articles are not introduced on a regular basis. In other languages, however, these may be open class words, and pronouns could be created relatively easily and regularly.
Even though the basic concept behind a closed class involves a lack of development of new words, there are usually changes within this class. The change is just much slower than open class words. This can be seen quite simply in English: new nouns and verbs are introduced quite frequently, usually through common use of new words, borrowing of words from other languages, and introduction of new words based on existing words being modified in previously unused ways.
Pronouns, on the other hand, have been quite stable for some time, though there are numerous examples of old pronouns that have left the English language such as “thee,” “thy,” and “thou.” The elimination of “ye” as the second person plural pronoun has since left an opening in the English language. This has been filled colloquially with words such as “youse,” “yinz,” and “y’all,” which have all failed to be adopted into broader use due to the closed nature of pronouns in English.