## Spring 2012

#### Friday Feb 17, 16.00 - 17.30: Alex Oliver (Cambridge)

#### A Theory of Plural Descriptions

Everybody knows that Russell had a theory of definite descriptions. Not everybody realises that he had two: one for singular descriptions (the author of 'On Denoting'), another for plural descriptions (the co-authors of Principia Mathematica). After examining Russell's own ideas, I shall propose a new theory of descriptions which covers both singular and plural cases, and which covers cases where the predicate embedded in the description is collective (the logicians who wrote Principia Mathematica) as well as distributive (the logicians who smoke). The theory contrasts sharply with Richard Sharvy's influential account. I shall conclude by explaining how the theory accommodates so-called 'higher-level' plurality, in which the description does not simply denote one thing or many.#### Friday March 9, 16.00 - 17.30: Keith Stenning (Edinburgh)

### The psychology and the logic of the syllogism

There seems to be a resurgence of interest in the (categorial) syllogism---it provides a microcosm for the study of logic, of mental grasp of logic, and of teaching logic.

It is clear that psychology needs a much more broadly based approach to the syllogism than it has taken so far---essentially studies of peoples' classical logical theorem provers for this fragment. What mental grasp of syllogistic logic do `logically naive' subjects have? Stenning & Yule proposed that the `conclusion generation task' which has dominated psychological studies, is interpreted in at least two logically quite distinct ways, so psychologists have not even got to grips with what task their subjects are trying to perform. And this psychological insight suggests the logical possibility of more than one interpretation of the syllogism be taken seriously.

The present talk will summarise the (Stenning & Yule 1997) account of the close relation between defeasible and classical understandings of syllogistic tasks. `Ekthesis' (Aristotle's analogue of universal instantiation?) is a classically valid reasoning pattern which is closely related to defeasible understandings. The talk will then ask how these two logical interpretations can be teased apart experimentally, and illustrate it's answer with some preliminary results from a first experimental foray, coincidentally conducted on Amsterdam logic-students-to-be.

**Thursday** April 5, 16.00 - 17.30: Greg Restall (Melbourne) **ROOM D1.113 at Science Park**

### Sequent Systems and Defining Rules

In this talk I will explain how it can be that inference rules can be used to define a class of concepts, and why there are at least three grades of logical complexity (propositional connectives, quantifiers, and modals), depending on the kinds of discourse features exploited in those rules. I'll then explain how concepts characterised by “defining rules” (which I’ll precisely characterise) have a number of important features, such as admitting a uniform cut elimination argument.

#### Friday April 13, **16.15** - 17.30: Katja Jasinskaja (ZAS, Berlin)

### The symmetry problem and the symmetry principle

The symmetry problem is a problem that arises in many approaches to the derivation of Quantity-based pragmatic effects (scalar implicatures, exhaustivity) that are based on reasoning with alternatives (i.e. in classical Gricean pragmatics, in particular). When a sentence S has two stronger alternatives S1 and S2 which contradict each other (symmetric alternatives), neither the implicature [not S1] nor the implicature [not S2] can be derived. For example, S = "John ate some of the apples", S1 = "John ate all of the apples", S2 = "John ate some but not all of the apples". The symmetry problem consists in ruling out one of the symmetric alternatives so as to match the empirical pattern of quantity implicatures.

In this talk I will argue that sometimes symmetry is a welcome property, which helps explain the absence of standard exhaustivity implicatures, for instance, in negative and mixed answers to positive wh-questions, as in: "Who came to the party? Not Mary.", which neither implies that John, Bill, etc. did not come, nor that they came (see esp. Spector, 2005). This approach has non-trivial implications for the general architecture of a theory of quantity-based pragmatic effects. It establishes a preference for theories that do have the symmetry problem, but provide a general mechanism to break symmetry, as well as a special mechanism to bring symmetry back where needed, over theories that do not have the problem in the first place, such as various versions of predicate circumscription.

#### Friday April 27, 16.00 - 17.30: Edgar Onea (Goettingen)

#### Friday May 11, 16.00 - 17.30: Yacin Hamami (Brussels)

### Towards an Inquisitive Approach to Interrogative Inquiry

Interrogative inquiry refers to the process of knowledge-seeking by questioning. In this talk, we propose to investigate the process of interrogative inquiry in the context of conversations by developing a formalization of interrogative inquiry based on inquisitive semantics and pragmatics. This is motivated by the capacity of inquisitive semantics to provide a semantic account of questions and answers in natural language, and the capacity of inquisitive pragmatics to provide a pragmatic account of the behavior of questions and answers in conversations. We will begin the talk by a presentation of the modelling of questions and answers in the inquisitive framework. Then, after a brief comparison of the inquisitive account of questions with Hintikka's treatment of questions in the Interrogative Model of Inquiry (IMI), we will discuss and define the notion of interrogative rule which aims to characterize the question-answer steps that one can make in an interrogative inquiry. We will then put the interrogative rule into a temporal perspective, by introducing the notion of interrogative protocol, which aims to govern interrogative inquiry as a temporal process. The notion of interrogative protocol enables us to reach formal definitions of the notion of interrogative inquiry and the associated logical notion of interrogative consequence, that we illustrate with some concrete examples. Our framework thus defined allows then for a formal logical and computational study of the process of interrogative inquiry. On the logical side, we relate the notion of interrogative consequence with the ones of distributed information and yes-no question. On the computational side, we shape the bases of a computational investigation of interrogative inquiry. From this computational perspective, we propose to revisit the so-called strategic aspects of inquiry, one of the main themes of Hintikka's IMI, from an algorithmic point of view. We will end the talk with some concluding remarks and suggestions for further works.

#### Friday June 1, 16.00 - 17.30: Stefan Wintein (Tilburg)

### Playing with truth

In this talk, I present a snapshot of my PhD thesis Playing with Truth, which is a collection of papers that revolve around a single topic: that of self-referential truth. The talk will focus on the joint rationale of the three frameworks for truth that are developed in the thesis, which are:

1) Assertoric semantics.

2) The method of closure games.

3) The strict-tolerant calculus.

Assertoric semantics and the method of closure games are semantic valuation tools that are used to define theories of truth. The strict-tolerant calculus is a signed tableau calculus that can be used to obtain syntactic characterizations of various consequence relations that are induced by those theories. Assertoric semantics can be understood as a semantic counterpart of the strict-tolerant calculus and the method of closure games as a refinement of assertoric semantics. In a

sense then, all three frameworks have a `` tableau-like’’ character. In each of our frameworks, the (tableau-like) rules, including those of the truth predicate are interpreted as assertoric rules, whereas the (tableau-like) closure conditions are interpreted as assertoric norms, i.e., as norms that govern the practice of asserting and denying. In a nutshell, the three frameworks echo the assertoric conception of truth that I develop in my thesis. In the talk, we will articulate the relations between the three frameworks and the main results pertaining to them. However, the focus will be on applications of the frameworks. In particular, we will illustrate how:

i) Assertoric semantics can be used to argue for the claim that self-referential truth has

computational power.

ii) Assertoric semantics and the strict-tolerant calculus jointly shed light on the strict-

tolerant conception of truth, which is a novel conception of truth that has recently

been proposed in joint work of Cobreros, Egré, Ripley and van Rooij.