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Symposium in honour of Göran Sundholm

Friday 6 September 2019
P.J. Veth
Nonnensteeg 1-3
2311 VJ Leiden

The Institute of Philosophy, Leiden University, announces a symposium in honour of Göran Sundholm on the day of his valedictory lecture, September 6, 2019.

The valedictory lecture will take place at 16.00 hours in the Groot Auditorium of the Academy Building.
Please register for this event on this page.

All are welcome!

09.45 coffee  
10.00 - 11.00 Per Martin-Löf ‘Epistemic assumptions: are they assumed to be backwards vindicated or forwards vindicable?’
11.15 - 12.15 Maria van der Schaar ‘Illusion, blindness and the dead man; a phenomenological account of modification’
13.30 - 14.30 Ansten Klev ‘Identity: propositional, criterial, definitional’


Per Martin-Löf


Per Martin-Löf is an emeritus professor of logic at the University of Stockholm.


In a paper from 1997, entitled Implicit epistemic aspects of constructive logic, Göran Sundholm introduced the term epistemic assumption for the assumptions with which the semantic (contentual) justification of a formal rule of inference invariably begins. The question to be discussed is whether these epistemic assumptions are assumed to be demonstrated or merely to be correctly (properly) asserted in the semantic (contentual) sense. I shall favour the second alternative.


Maria van der Schaar


Maria van der Schaar has been a colleague of Göran Sundholm for 30 years, and is working with him on the Epistemic Foundation of Logic.


Whereas calling someone a ‘Parisian friend’ adds something to calling him a ‘friend’, calling someone a ‘false friend’ is not simply an addition, for a false friend is not a friend at all. The term ‘false’ in this context is a modifying term. The logical behaviour of these terms have interested philosophers and logicians since Aristotle (‘it is false to call a dead man a man’, De Interpretatione, ch. 11 21a21).

A phenomenological account of modification is proposed to account for the conceptual relation between friend and false friend. This account can be used to illuminate the conceptual relation between philosophical concepts, such as that between proof and invalid proof, and that between perception and illusion.

Ansten Klev


Ansten Klev is a post-doc at the Academy of Sciences of the Czech Republic, Institute of Philosophy.


Propositional identity is the familiar notion of identity expressed by the identity formulae, a = b, of predicate logic. Criterial identity is the notion of identity that is involved in the criterion of identity for a category. Definitional identity is the relation that holds between meaningful expressions, or structured meanings, that are identical by definition. In the paper "Identity: absolute, criterial, propositional" Göran Sundholm argues that, since propositional identity is defined only over a category, which itself is defined only if a criterion of identity has been given for it, criterial identity must be conceptually prior to propositional identity. I will first rehearse Sundholm's argument and then note that a similar point can be made about definitional identity: it as well is conceptually prior to propositional identity. Nothing in the arguments given forces us to identify criterial with definitional identity. But if we do identify them, as is done in the meaning explanations for Martin-Löf's type theory, we are led to a novel position in the ontology of mathematics, namely the view that mathematical objects are to be understood as meaningful expressions.


Ansten Klev completed an MPhil as well as a PhD at Leiden University with Göran Sundholm as supervisor. He is now a postdoc at the Czech Academy of Sciences.

For further information, please send a message to m.v.d.schaar@phil.leidenuniv.nl

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