This dissertation explores the syntax and semantics of positive and comparative gradable adjectives. A detailed study of intransitive (tall) and transitive (patient with Mary) adjectives is provided with special emphasis on phrases that express the standard of comparison, such as tall for a jockey, tall compared to Bill, and taller than Bill. It is shown that standard expressions, surprisingly, behave differently both syntactically and semantically. There are four main conclusions. First, a syntactic analysis is provided in which all standard expressions are introduced by unique degree morphemes in the extended projection of the adjective. Each morpheme and the standard expression that it introduces is ordered such that for-PP's are introduced just above the adjective, followed by compared-to phrases and then comparatives. Thematic-PP's which denote the object of transitive adjectives are shown to be introduced in the extended projections as well, but interestingly, they are introduced between the for-PP and the compared-to phrase. Second, a neo-Davidsonian, event-style analysis is provided that completely separates the internal and external arguments of adjectives. Instead, gradable adjectives are treated as predicates of events (or states), simply. Arguments of the adjective are assigned theta-roles in the syntax and are integrated into the logical form through via conjunction. Third, all other parts of the meanings of positive and comparative adjectives are put into the denotation of the degree morphemes. This includes the comparison relation and the measure function. Thus, gradable adjectives are treated as the same semantic type as other adjectives and other predicates. And fourth, it is shown that positive adjectives are fundamentally different from comparative adjectives in a semantic sense. This is surprising because standard semantic theories of positives treat them as implicit comparatives. The primary difference is that positives are vague in a way that comparatives are not. It is shown that the difference is not a matter of context dependence as suggested in Fara (2000). Instead, it is suggested that the comparative morpheme is responsible for this difference. Therefore, grammatical processes can interact with vagueness in at least one way; they can reduce it.