**23 September**: Room DZ 6

**Vague Desire: the Sorites and Money Pump**

David Etlin,

University of Leuven

**14 October**: Room DZ 10

**The Barcan Formula and Completeness of First-Order Modal Logic**

Eric Pacuit,

TiLPS

In this talk, we will survey some recent work on completeness of first-order

modal logics. In particular we will look at the role that the Barcan

formula(s) play in various completeness proofs. We will focus on non-normal

systems (cf. “First-Order Classical Modal Logic” by Horacio Arlo-Costa and

Eric Pacuit, Studia Logica 84(2), 2006) and general completeness theorems

(cf. “A General Semantics for Quantified Modal Logic” by Robert Goldblatt

and Edwin Mares, Advances in Modal Logic 6, 2006). Time permitting we will

also look at alternative semantics for the first-order modal language.

**28 October**: Room DZ 8

**Agreeing to Disagree in Probabilistic Dynamic Epistemic Logic**

Lorenz Demey,

University of Leuven, ILLC

In this talk I will discuss Aumann’s celebrated agreeing to disagree

theorem from the perspective of probabilistic dynamic epistemic logic.

I will first introduce Aumann’s own formal statement of the theorem, and

its intuitive motivation. Next I will introduce probabilistic Kripke

models and various ways of updating them. These tools are then used to

model several versions of the agreement theorem. I will also introduce

sound and complete agreement logics. On the basis of these technical

results I will make some philosophical/methodological points about the

agreement theorem, in particular about the role of common knowledge and

the underlying dynamics. If time permits, I will also compare my approach

with another way of modeling the agreement theorem in DEL, which has been

developed by Dégremont and Roy.

**11 November**: Room DZ 6

**Adjectives, Scales and Zeros**

Galit Weidman Sassoon,

ILLC

Degree questions such as “how tall is John?” and equatives such as “John is

as tall as Mary” do not imply that John is tall, while their negative

counterparts (“how short is John?” and “John is as short as Mary”) do imply

that John is short. Existing theories attempt to explain this by means of a

competition between unmarked (positive) and marked (negative) antonyms, and

by means of a null morpheme that introduces a standard-variable into the

derivation (in analogy with the standard analysis of the positive form “John

is tall/short”; cf. Rett 2007). This talk attempts to present data that

challenge these theories, as well as an alternative analysis for the facts

based on the existence of an absolute zero or its lack thereof, in the

interpretation of, e.g., ‘tall’ and ‘short’, respectively. Implications for

additional dominant linguistic analyses of scalar adjectives will be

discussed, pertaining to differences between absolute and relative

adjectives (cf. Winter and Rothstein 2005; Kennedy and McNally 2005; Kennedy

2007).

**9 December**: Room DZ 6

**Sense and Circularity: Recursion in Higher Order Logic**

Reinhard Muskens,

TiLPS

In this talk I will report on ongoing work with the goal of developing a

higher order logic that is not only truly intensional, in the sense that

necessarily coextensional objects need not have the same properties, but in

which it is also possible to model Fregean senses as *algorithms*

along the lines of Moschovakis [1]. In this influential paper Moschovakis

succeeds in combining an account of the procedural character of meaning with

an account of circular statements such as the Liar and

Truthteller—these circular statements are associated with looping

algorithms. Moschovakis [1] uses a first order logic, while higher order

logics are more suitable for natural language description. This is remedied

in Moschovakis [2] by adding recursors to the simply typed lambda calculus,

but while [2] succeeds admirably in modeling the procedural character of

language, the possibility of modeling circularity is lost, as an acyclicity

requirement is necessary. My aim here is to remedy this situation. I will

discuss the idea of taking the intensional logic of [5] (‘classical higher

order logic minus Extensionality’) and partializing it along the lines of

[3]. In partial logics some extra connectives become available, but terms in

the classical part of the language exhibit monotonicity behaviour with

respect to the definedness ordering. I will discuss the possibility of

defining a sublanguage which contains the classical fragment but

additionally has a simultaneous fixpoint operator similar to Moschovakis’

and using it to model procedurality and circularity in ordinary language.