Definition
A "major form class" refers to the four main categories of words that carry the most significant meaning in a sentence: nouns, verbs, adjectives, and adverbs. These classes are considered "open," meaning new words are constantly being added to them (think of new slang or technological terms). They contrast with minor form classes (like prepositions or conjunctions), which have more limited membership. Major form classes provide the core content of sentences. They describe what is being talked about (nouns), what is happening (verbs), and the qualities or manner of things (adjectives and adverbs).