Conversational presuppositions: Presupposition as defeasible inference

In this paper, I will try to support the admittedly controversial claim that presuppositions are normally defeasible inferences, taking the lead from Levinson, Stephen C. 1983.

Textual Entailment

Textual entailment is a binary relation between two natural-language texts (called ‘text’ and ‘hypothesis’), where readers of the ‘text’ would agree the ‘hypothesis’ is most likely true (Peter is snoring → A man sleeps). Its recognition requires an account of linguistic variability ( an event may be realized in different ways, e.g. Peter buys the car ↔ The car is purchased by Peter) and of relationships between events (e.g. Peter buys the car → Peter owns the car). Unlike logics-based inference, textual entailment also covers cases of probable but still defeasible entailment (A hurricane hit Peter’s town → Peter’s town was damaged). Since human common-sense reasoning often involves such defeasible inferences, textual entailment is of considerable interest for real-world language processing tasks, as a generic, application-independent framework for semantic inference. This chapter discusses the history of textual entailment, approaches to recognizing it, and its integration in various NLP tasks.

Epistemic particles and perfomativity

The German discourse particles ‘ja’ and ‘doch’ both mark the information expressed by their host sentence as somehow given, obvious, or uncontroversial (McCready & Zimmermann 2011 call them ‘epistemic particles’). Two things are puzzling: (i) despite its ‘epistemic’ nature, ‘doch’ can appear in imperatives and with performative modals; (ii) despite their similarity, ‘ja’ is unacceptable in imperatives and forces a descriptive reading of modal verbs. We explain (i) by assuming that the performativity of modalized propositions depends on certain contextual constellations which may conflict with constraints imposed by the particles. To account for (ii), we offer an analysis for ‘ja’ and ‘doch’ that explains the inviolable ban against ‘ja’ (but not ‘doch’) from performative modal contexts in terms of defeasible inferences about the context.

Epistemic particles and perfomativity

The German discourse particles ‘ja’ and ‘doch’ both mark the information expressed by their host sentence as somehow given, obvious, or uncontroversial (McCready & Zimmermann 2011 call them ‘epistemic particles’). Two things are puzzling: (i) despite its ‘epistemic’ nature, ‘doch’ can appear in imperatives and with performative modals; (ii) despite their similarity, ‘ja’ is unacceptable in imperatives and forces a descriptive reading of modal verbs. We explain (i) by assuming that the performativity of modalized propositions depends on certain contextual constellations which may conflict with constraints imposed by the particles. To account for (ii), we offer an analysis for ‘ja’ and ‘doch’ that explains the inviolable ban against ‘ja’ (but not ‘doch’) from performative modal contexts in terms of defeasible inferences about the context.

Reasoning with Exceptions: An Event-related Brain Potentials Study

Defeasible inferences are inferences that can be revised in the light of new information. Although defeasible inferences are pervasive in everyday communication, little is known about how and when they are processed by the brain. This study examined the electrophysiological signature of defeasible reasoning using a modified version of the suppression task. Participants were presented with conditional inferences (of the type “if p, then q; p, therefore q”) that were preceded by a congruent or a disabling context. The disabling context contained a possible exception or precondition that prevented people from drawing the conclusion. Acceptability of the conclusion was indeed lower in the disabling condition compared to the congruent condition. Further, we found a large sustained negativity at the conclusion of the disabling condition relative to the congruent condition, which started around 250 msec and was persistent throughout the entire epoch. Possible accounts for the observed effect are discussed.