operator theory of adverbs a theory that treats adverbs and other predicate modifiers as predicate-forming operators on predicates. The theory expands the syntax of first-order logic by adding operators of various degrees, and makes corresponding additions to the semantics. Romane Clark, Terence Parsons, and Richard Montague (with Hans Kamp) developed the theory independently in the early 1970s. For example: ‘John runs quickly through the kitchen’ contains a simple one-place predicate, ‘runs’ (applied to John); a zero-place operator, ‘quickly’, and a one-place operator, ‘through ()’ (with ‘the kitchen’ filling its place). The logical form of the sentence becomes [O11(a) [O20 [P(b)]]], which can be read: [through (the kitchen) [quickly [runs (John)]]]. Semantically ‘quickly’ will be associated with an operation that takes us from the extension of ‘runs’ to a subset of that extension. ‘John runs quickly’ will imply ‘John runs’. ‘Through (the kitchen)’ and other operators are handled similarly. The wide variety of predicate modifiers complicates the inferential conditions and semantics of the operators. ‘John is finally done’ implies ‘John is done’. ‘John is nearly done’ implies ‘John is not done’. Clark tries to distinguish various types of predicate modifiers and provides a different semantic analysis for operators of different sorts. The theory can easily characterize syntactic aspects of predicate modifier iteration. In addition, after being modified the original predicates remain as predicates, and maintain their original degree. Further, there is no need to force John’s running into subject position as might be the case if we try to make ‘quickly’ an ordinary predicate. T.J.D.