Interpreting Linguistic Behavior with Possible World Models Johannes Marti Abstract: Interpreting Linguistic Behavior with Possible World Models Johannes Marti In this thesis I develop an account of radical interpretation using the possible world framework to model beliefs and meanings. I prove representation results which show that if the linguistic behavior of some subject satisfies certain conditions then it can be taken to arise from a certain type of possible world model for belief and meaning. These results are analogous to representation theorems in decision theory which show that if the choice behavior of some subject satisfies certain conditions then it arises from expected utility maximization with respect to some subjective probability and utility functions. I consider multiple accounts that differ in the details of the modeling. They have in common that they all consist of the following five steps: First, a definition of the possible world models that are used. In simple cases they contain a set of possible worlds to represent the belief state of some subject and a function mapping sentences to sets of worlds to represent meanings. Second, a definition of some notion of linguistic behavior. In the basic case I take a linguistic behavior to be a set of sentences in the language of the subject which is thought of as the set of sentences the subject accepts in some situation. Third, a definition of the linguistic behavior generated by some possible world model. This definition is a formalization of the idea that the subject accepts some sentence in some situation if the sentence expresses a proposition that the subject believes in that situation. Forth, a specification of further assumptions that we are making about the subject. This includes assumptions about the meaning of some expressions in the language of the subject, such as for instance the propositional connectives, or assumptions about some of the subject's beliefs in certain situations, such as for instance the beliefs that the subject obtains from perception. Fifth, a representation results that gives necessary and sufficient conditions for a linguistic behavior to be the behavior generated by some model that satisfies the additional assumptions made in the forth step. In the first part of the thesis I develop the basic account of interpretation, which is extended later, and consider different possibilities for modeling beliefs. The most refined account that I discuss uses a plausibility order over possible worlds to model how the subject revises her beliefs in light of new evidence. In the second part of the thesis I explore different possibilities for modeling meanings. I distinguish between a disquotational and a metasemantic acceptance principle. According to the disquotational acceptance principle the subject accepts a sentence if and only if according to the semantic facts that obtain at the actual world the sentence expresses a proposition that the subject believes. According to the metasemantic acceptance principle the subject accepts a sentences if and only if the subject believes that the sentence expresses a true proposition. The distinction between disquotational and metasemantic acceptance crucially influences the formal model of meaning. I demonstrate this by discussing two concrete problems for a theory of interpretation that are solved differently depending on which version of the acceptance principle we choose. The first is the problem of accounting for situations in which the subject has complete knowledge about all the relevant facts but still does not accept some sentence nor accepts its negation. On the metasemantic account of acceptance such cases are situations in which the subject is uncertain about the semantic facts that determine the meaning of the sentence. With a disquotational account of acceptance one can only account for such cases if one employs a notion of meaning according to which the truth value of some sentence at some possible world can remain indeterminate. The second is the problem of necessity a posteriori that arises when the subject's acceptance of sentences containing a necessity modality changes as she obtains new beliefs about the world. I argue that the distinction between disquotational and metasemantic acceptance corresponds to the distinction between the epistemic and the metasemantic interpretation of two-dimensional semantics.