In each language the dependency relation among words gives rise to syntactic categories in which the allowable arguments of an operator are defined in terms of their dependency requirements. Class N contains words (e.g. "John", "boots") that do not require the presence of other words. Class ON contains the words (e.g. "stumble") that require exactly one word of type N. Class ONN contains the words (e.g. "wear") that require two words of type N. Class OOO contains the words (e.g. "because") that require two words of type O, as in "John stumbles because John wears boots". Other classes include OO (e.g. "is possible"), ONNN (e.g. "put"), OON (e.g. "with"), ONO (e.g. "know"), ONNO (e.g. "ask") and ONOO (e.g. "attribute").