Ambiguity and vagueness are two varieties of interpretive uncertainty which are often discussed together, but are distinct both in their essential features and in their signifi cance for semantic theory and the philosophy of language. Ambiguity involves uncertainty about mappings between levels of representation with different structural characteristics, while vagueness involves uncertainty about the actual meanings of particular terms. This article examines ambiguity and vagueness in turn, providing a detailed picture of their empirical characteristics and the diagnostics for identifying them, and explaining their signifi cance for theories of meaning. Although this article continues the tradition of discussing ambiguity and vagueness together, one of its goals is to emphasize the ways that these phenomena are distinct in their empirical properties, in the factors that give rise to them, and in the analytical tools that can be brought to bear on them.23. Ambiguity and vagueness: An overview 509 has an ability to make people laugh ("funny ha-ha'') or that she tends to display odd or unusual behavior ("funny strange''). Similarly, (1b) can be used to convey the information that Julian's brother has a relatively high degree of weight, or that he is somehow serious, ponderous, or full of gravitas. That these pairs of interpretations involve distinct truth conditions is shown by the fact that we can use the same term (or, more accurately, the same bits of phonology) to say something that is true and something that is false of the same state of affairs, as in (4) (Zwicky & Sadock 1975).(4) Sterling's cousin used to make people laugh with everything she did, though she was never in any way strange or unusual. She was funny without being funny. Lately, however, she has started behaving oddly, and has lost much of her sense of humor. Now she's funny but not very funny.Both examples also manifest an ambiguity in the nature of the relation that holds between the genitive-marked nominal in the possessive construction and the denotation of the whole possessive DP; cf. article 45 (Barker) Possessives and relational nouns. While the most salient relations are the familial ones expressed by the respective head nouns (cousin of and brother of ), it is possible to understand these sentences as establishing different relations. For example, if Julian is one of several tutors working with a family of underachieving brothers, we could use (1b) as a way of saying something about the brother who has been assigned to Julian, without in any way implying that Julian himself stands in the brother of relation to anyone. (He could be an only child.) Even after we settle on a particular set of conditions of application for the ambiguous terms in (1a) and (1b) (e.g. that we mean "funny ha-ha'' by funny or are using heavy to describe an object's weight), a third type of uncertainty remains about precisely what properties these terms ascribe to the objects to which they are applied, and possibly about whether these terms can even be applied in ...