Nicholas Asher

We define an order independent version of default unification on typed feature structures. The operation is one where default information in a feature structure typed with a more specific type, will override default information in a feature structure typed with a more general type, where specificity is defined by the subtyping relation in the type hierarchy. The operation is also able to handle feature structures where reentrancies are default. We provide a formal semantics, prove order independence and demonstrate the utility of this version of default unification in several linguistic applications. First, we show how it can be used to define multiple orthogonal default inheritance in the lexicon in a fully declarative fashion. Secondly, we show how default lexical specifications (introduced via default lexical inheritance) can be made to usefully persist beyond the lexicon and interact with syntagmatic rules. Finally, we outline how persistent default unification might underpin default feature propagation principles and a more restrictive and constraint-based approach to lexical rules.

Most models of rational action assume that all possible states and actions are pre-defined and that preferences change only when beliefs do. But several decision and game problems lack these features, calling for a dynamic model of preferences: preferences can change when unforeseen possibilities come to light or when there is no specifiable or measurable change in belief. We propose a formally precise dynamic model of preferences that extends an existing static model. Our axioms for updating preferences preserve consistency while minimising change, like Hansson’s :1–28, 1995). But unlike prior models of preference change, ours supports default reasoning with partial preference information, which is essential to handle decision problems where the decision tree isn’t surveyable. We also show that our model avoids problems for other models of preference change discussed in Spohn.

’s glue logic for computing logical form dynamic. This allows us to model a dialogue agent’s understanding of what the update of the semantic representation of the dialogue would be after his next contribution, including the effects of the rhetorical moves that he is contemplating performing next. This is a pre-requisite for developing a model of how agents reason about what to say next. We make the glue logic dynamic by using a dynamic public announcement logic ( pal ). We extend pal with a particular variety of default reasoning suited to reasoning about discourse—this default reasoning being an essential component of inferring the pragmatic effects of one’s dialogue moves. We add to the pal language a new type of announcement, known as ceteris paribus announcement, and this is used to model how an agent anticipates the (default) pragmatic effects of his next dialogue move. Our extended pal validates certain intuitive patterns of default inference that existing pal s for practical reasoning do not. We prove that the dynamic glue logic has a pspace validity problem, and as such is no more complex than pal with multiple $${\square}$$ operators.

A fundamental question in reasoning about change is, what information does a reasoning agent infer about later times from earlier times? I will argue that reasoning about change by an agent is to be modeled in terms of the persistence of the agent''s beliefs over time rather than the persistence of truth and that such persistence is explained by pragmatic factors about how agents acquire information from other agents rather than by general principles of persistence about states of the world. AI accounts of persistence have focused on closed world examples of change, in which the agent believes that the truth of a proposition is unaltered so long as he or she has no evidence that it has been changed. AI principles of persistence seem plausible in a closed world where one assumes the agent knows everything that is happening. If one drops the assumption of omniscience, however, the analysis of persistence is implausible. To get a good account of persistence and reasoning about change, I argue we should examine open world examples of change, in which the agent is ignorant of some of the changes occurring in the world. In open world examples of change, persistence must be formulated, I argue, as a pragmatic principle about the persistence of beliefs. After elaborating my criticisms of current accounts of persistence, I examine how such pragmatic principles fare with the notorious examples of reasoning about action that have collectively characterized the so-called frame problem.

The purpose of this paper is to (a) show that the received view of the problem of quantificational subordination (QS) is incorrect, and that, consequently, existing solutions do not succeed in explaining the facts, and (b) provide a new account of QS. On the received view of QS within dynamic semantic frameworks, determiners treated as universal quantifiers (henceforth universal determiners) such as all, every, and each behave as barriers to inter-sentential anaphora yet allow anaphoric accessibility in a number of situations. We argue that universal determiners are not intrinsic anaphora barriers and that anaphoric accessibility under them is enabled factors including lexicon information and discourse effects of universal determiners. In support of this viewpoint, we first provide a data survey on the phenomena of QS and its interactions with plurals, rhetorical relations, and adverbial quantification. The results of the survey show that judgments of (naive) native English speakers on the QS examples are quite different from what is claimed in the literature. We argue that the various solutions in the literature, which in general accept that universal determiners are intrinsic anaphora barriers, fail to account for the facts from the survey data. We then describe the approach we adopt, which denies that universal determiners are anaphora barriers and reconstructs their semantics so that information in their scope can be released for anaphora. The constraints on QS noted in the literature we model in Segmented Discourse Representation Theory (SDRT) as conditions on the discourse relations which can hold between subordinated constituents. We show that this approach accounts for the QS data.

In this paper, we address several puzzles concerning speech acts, particularly indirect speech acts. We show how a formal semantictheory of discourse interpretation can be used to define speech acts and to avoid murky issues concerning the metaphysics of action. We provide a formally precise definition of indirect speech acts, including the subclass of so-called conventionalized indirect speech acts. This analysis draws heavily on parallels between phenomena at the speech act level and the lexical level. First, we argue that, just as co-predication shows that some words can behave linguistically as if they're `simultaneously' of incompatible semantic types, certain speech acts behave this way too. Secondly, as Horn and Bayer (1984) and others have suggested, both the lexicon and speech acts are subject to a principle of blocking or "preemption by synonymy": Conventionalized indirect speech acts can block their `paraphrases' from being interpreted as indirect speech acts, even if this interpretation is calculable from Gricean-style principles. We provide a formal model of this blocking, and compare it with existing accounts of lexical blocking.

This essay lays out a view of linguistic content in which discourse context plays an essential role. It provides a role for sentential content by using underspecification but argues that discourse level phenomena are essential not only to determining content but even grammaticality judgments in certain cases. It is thus argued that the traditional view which separates very strictly the areas of semantics — a context insensitive notion of meaning — and pragmatics — a non linguistic notion of speaker meaning — is inaccurate. In this line of thought, the paper pays a particular attention to hidden indexicals, anaphora and tense. The necessity of taking into account discursive parameters in order to solve semantic indeterminacy in such cases is argued for.

This essay is about a theory of belief and a theory of belief reports formulated within the framework of DR theory. DR theory’s treatment of definite and indefinite noun phrases leads to a superior treatment of belief reports involving singular terms. But it also provides something of even greater potential benefit to a treatment of belief: a theory of how recipients recover verbally encoded information and of what form such information must take. The use of this account of verbally encoded information causes a distinctive treatment of belief to emerge. I will focus here on an analysis within this framework of how beliefs arise from the acceptance of verbal information and how the process of belief formation interacts with the process of belief report interpretation.

In this paper, we offer a novel analysis of bridging, paying particular attention to definite descriptions. We argue that extant theories don't do justice to the way different knowledge resources interact. In line with Hobbs (1979), we claim that the rhetorical connections between the propositions introduced in the text play an important part. But our work is distinct from his in that we model how this source of information interacts with compositional and lexical semantics. We formalize bridging in a framework known as SDRT (Asher 1993). We demonstrate that this provides a richer, more accurate interpretation of definite descriptions than has been offered so far.

We provide examples of plurals related to ambiguity and anaphora that pose problems or are counterexamples for current approaches to plurals. We then propose a dynamic semantics based on an extension of dynamic predicate logic to handle these examples. On our theory, different readings of sentences or discourses containing plurals don’t arise from a postulated ambiguity of plural terms or predicates applying to plural DPs, but follow rather from different types of dynamic transitions that manipulate inputs and outputs from formulas or discourse constituents. Many aspects of meaning can affect the type dynamic transitions: the lexical semantics of predicates to the left and right of a transition, and number features of DPs and discourse constraints like parallelism.

When two people engage in a conversation, knowingly or unknowingly, they are playing a game. Players of such games have diverse objectives, or winning conditions: an applicant trying to convince her potential employer of her eligibility over that of a competitor, a prosecutor trying to convict a defendant, a politician trying to convince an electorate in a political debate, and so on. We argue that infinitary games offer a natural model for many structural characteristics of such conversations. We call such games message exchange games, and we compare them to existing game theoretic frameworks used in linguistics—for example, signaling games—and show that message exchange games are needed to handle non-cooperative conversation. In this paper, we concentrate on conversational games where players’ interests are opposed. We provide a taxonomy of conversations based on their winning conditions, and we investigate some essential features of winning conditions like consistency and what we call rhetorical cooperativity. We show that these features make our games decomposition sensitive, a property we define formally in the paper. We show that this property has far-reaching implications for the existence of winning strategies and their complexity. There is a class of winning conditions for which message exchange games are equivalent to Banach- Mazur games, which have been extensively studied and enjoy nice topological results. But decomposition sensitive goals are much more the norm and much more interesting linguistically and philosophically.

This volume is about abstract objects and the ways we refer to them in natural language. Asher develops a semantical and metaphysical analysis of these entities in two stages. The first reflects the rich ontology of abstract objects necessitated by the forms of language in which we think and speak. A second level of analysis maps the ontology of natural language metaphysics onto a sparser domain--a more systematic realm of abstract objects that are fully analyzed. This second level reflects the commitments of real metaphysics. The models for these commitments assign truth conditions to natural language discourse. Annotation copyright by Book News, Inc., Portland, OR.