Open class (linguistics)

In linguistics, an open class (or open word class) is a word class that accepts the addition of new items, through such processes as compounding, derivation, coining, borrowing, etc. Typical open word classes are nouns, verbs and adjectives.

Open-class words are not considered part of the core language and as such they can be changed, replaced or dropped from the common lexicon, which can encompass many thousands of them. For living languages, this change is noticeable within an individual lifespan, and usually faster. Closed-class words, on the other hand, are always relatively few and resistant to change.

English open word classes
In English, open classes include the following parts of speech:
 * nouns
 * verbs (except auxiliary verbs)
 * adjectives
 * adverbs
 * interjections

Interjections are formed as new words standing in for sounds, and are added not only from technical backgrounds, but also from sources such as comics and subtitling. It is in these that one will encounter the noises of motor revving, sirens, mechanical sounds and violence, continuously being updated. Examples here are: vroom!, va-va-voom!, zonk!, grrh!, and so on.

Slang is one of the major sources of new open-class words. Slang words appear first in small segments of the population, and then spread to the mainstream speaking community and become standard, or fade after a period of being in fashion.

In some constructed languages, for instance Volapük, prepositions and conjunctions are open-class words as they can be formed by the use of affixes from root nouns or verbs.

==See also
 * Closed class
 * Form class (language)