Closed Class (definition)
A semantic class of words whose syntactic function in a sentence is to denote the relationship between the words in the sentence that are part of the open class, such as nouns and verbs. The closed class is so named because it is very rarely a group of words that can be added to. In English, the closed class, includes words like if, and, over, under, in. The open class includes nouns and verbs, which can always be added to, the word "google" is a good example of this. In the sentence, "If George had googled the blorp, he would have known what it was." the words George, googled, blorp and known can be replaced: "If Patty had watched the tinker she would have understood what it was." In contrast, replacing words like "if" "the" "had" etc. is much more difficult because they are members of the closed class.
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