sentences with scope ambiguities. Exceptional scope While most operators are unable to scope out of an island, others can. For instance, the indefinite "a" in the sentence below can take scope outside of its surface position inside an "if"-clause. This sentence can mean that there is a particular relative who must die for the speaker to get a house. If a relative of mine dies, I will inherit a house. Examples of this sort have been used to argue that indefinites do not have standard generalized quantifier denotations. On the choice function approach proposed by Tanya Reinhart, indefinites contribute a variable over choice functions which can be existentially closed at any point higher in the structure. Angelika Kratzer proposed another choice function-based theory, which is similar to Reinhart's except that the choice function variable is left free. Recent work such as Charlow (2020) treats indefinites as denoting sets of individuals which can be type shifted so that they take scope in a manner similar to Karttunen's (1977) alternative-based mechanism for wh-questions. Formal approaches to scope The structural view of scope is one influential view which posits a close relationship between syntax and semantics. This approach is characterized by the following hypothesis, first formulated by Tanya Reinhart: Hypothesis about scope and domain: The semantic scope of an operator corresponds to the position of the item which expresses it at some level of syntactic representation. This view is widely adopted in generative approaches such as that of Heim and Kratzer (1998). In these approaches, the relevant syntactic level is logical form and the syntactic notion which corresponds to semantic scope is typically identified as c-command. In structural approaches, discrepancies between an expression's surface position and its semantic scope are explained by syntactic movement operations such as quantifier raising. The movement approach is motivated in large part by the fact that quantifier scope seems to obey many of the same restrictions that movement does, e.g. islands. One prominent alternative to the structural view is the type shifting view first proposed by Barbara Partee and Mats Rooth. This approach uses type shifters to govern scopal relations. Since type shifters are applied during the process of semantic interpretation, this approach allows scopal relations to be partly independent of syntactic structure. The type shifting approach serves as the basis of many recent proposals for exceptional scope, split scope, and other troublesome scope-related phenomena. See also Continuation-passing