From 22 April 2016 to 25 April 2016

Retirement Albert Visser

Prof. dr. Albert Visser
Prof. Albert Visser

In the spring of 2016 Prof. Albert Visser (Philosophy) will retire. He has been a professor in Logic and the Foundations of Mathematics at Utrecht University for more than a decade. Since September 2015 he is also a Faculty Professor at the Faculty of Humanities. There will be two days of celebrations in honour of his long and distinguished career. Registration is now open.

On Friday 22 April 2016, there will be a workshop dedicated to his scientific work, with speakers from the various areas that Visser has contributed to. This event will take place in the Kanunnikenzaal of the University Hall (Academiegebouw).

On Monday 25 April 2016, there will be an afternoon of celebratory speeches by colleagues (starting at 13:00 in the Kanunnikenzaal of the University Hall), followed by Albert’s retirement speech at 16:15 in the Auditorium of the University Hall and a reception.

Prof. Albert Visser is one of the foremost logicians of our time. His research in fundamental logic and artificial intelligence – focusing on the relations between logic, mathematics and philosophy – has been influential across the world, and his research group has been assessed as 'excellent' by three subsequent national review committees. In addition, he has played a leading role in the development of the bachelor's programme in artificial intelligence (Kunstmatige intelligentie). All in all he has contributed significantly to education and research within the Faculty of Humanities.

Programme Friday 22 April

  • 9:30 - 10:15 Ali Enayat
  • 10:15 - 10:30 break
  • 10:30 - 11:15 Dick de Jong
  • 11:15 - 11:30 break
  • 11:30 - 12:15 Rick Nouwen
  • 12:15 - 13:30 lunch
  • 13:30 - 14:15 Volker Halbach
  • 14:15 - 14:30 break
  • 14:30 - 15:15 Volodya Shavrukov
  • 15:15 - 15:30 break
  • 15:30 - 16:15 Lev Beklemishev


Lev Beklemishev: Some abstract versions of Goedel's Second Incompleteness Theorem based on non-classical logics

We study abstract versions of Goedel's second incompleteness theorem and formulate generalizations of Loeb's derivability conditions that work for logics weaker than the classical one. We isolate the role of the contraction rule in Goedel's theorem and give a (toy) example of a system based on modal logic without contraction invalidating Goedel's argument.

Ali Enayat: Visser's Categorical Lens

Visser's majestic paper Categories of Theories and Interpretations introduced a novel framework to study interpretations through the lens of category theory. I will focus on certain insights offered by Visser's lens, including an enigmatic feature of Peano Arithmetic, and a select number of other canonical theories.

Volker Halbach: The seeds of doubt

It is often assumed that certain claims can be expressed in arithmetic. For instance, it is assumed that the consistency of Peano arithmetic can be expressed by an arithmetical sentence. Gödel described his sentence as a sentence that states its own unprovability. The arithmetic ∑_n-truth teller is said to claim its own ∑_n-truth. When constructing such sentences in arithmetic certain choices have to be made. In particular, one has to choose a coding scheme, a formula expressing provability or ∑_n-truth etc, and perhaps, a way to obtain self-reference. Different choices may yield sentences with different properties. I will provide some examples. Finally I will investigate whether are justified in describing the Gödel sentence as a sentence stating its own unprovability, the ∑_n-truth teller as claiming its own truth and so on for other sentences.

Volodya Shavrukov: Top of the Crop: Albert Visser on Σ₁-maximal extensions

We are going to dicuss Albert's contributions to the study of the modality whose accessibility relation is embeddability between models of Peano Arithetic, including extensions of the Orey–Hájek characterization and the Π¹₁-completeness of possible necessity. We review the special relation of this topic to the E-tree and to Σ₁-maximal Peano completions.

Dick de Jongh: Propositional logic, provability, intuitionism

Areas in propositional logic in which Albert Visser worked and some recent developments.

Rick Nouwen: The Damned and the Monoid

Since we hear or read sentences one bit at a time, it speaks for itself that interpretation is at least in part an incremental process. Still, most formal natural language semanticists study only the end-product of interpretation, i.e. the final meaning assigned to the sentence as a whole. The common assumption is that this meaning is derived compositionally and not incrementally. In his work on dynamic semantics, Visser (see especially Visser and Vermeulen 1996) aims to use the logical language of sentential and sub-sentential meanings to first and foremost model the interpretation process, and not just the end-product. In this talk I will avoid the tricky topic of the relation between incremental interpretation and sentential meaning and instead focus on a phenomenon where expressions contribute their full and final content in an undeniably incremental way. This concerns so-called expressives: words with instantaneous (often emotive) interpretative effects that escape the scope of operators in their environment. For example, in "John didn't lock the damned back door!", the expressive "damned" signals the speaker's agitation, but this signal is clearly not negated by the sentence negation "n't".

I will present an application of Visser's (2002) (quasi-)monoidal semantics of polarity switching to expressives, fully exploiting this framework's ability to represent streams of information. Although this exercise shows the potential of Visser's framework, I will also discuss possible technical and, more importantly, conceptual issues with an approach along these lines.

- Visser, A. (2002). 'The Donkey and the Monoid'. Journal of Logic, Language and Information 11, pp. 107–131.
- Visser, A. and C. Vermeulen (1996). 'Dynamic Bracketing and Discourse Representation'. Notre Dame Journal of Formal Logic 37, pp. 321–365

Start date and time
22 April 2016
End date and time
25 April 2016