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The Forum is open to everyone, including students, visitors, and faculty members from all departments and institutes!

The 60 minute lecture is followed by a 10 minute break and a 30-60 minute discussion. The language of presentation is English or Hungarian.


The scope of the Forum includes all aspects of theoretical philosophy, including:

  • logic and philosophy of formal sciences
  • philosophy of science
  • modern metaphysics
  • epistemology
  • philosophy of language
  • problems in history of philosophy and history of science, relevant to the above topics
  • particular issues in natural and social sciences, important for the discourses in the main scope of the Forum.



15 November (Wednesday) 5:00 PM  Room 226
Krisztina Kessel
Institute of Philosophy, Eötvös University, Budapest
  Extended Mind Theory and Counterarguments
In their 1989 paper entitled The extended mind Andy Clark and David Chalmers presented a new concept of externalism they called ‘active externalism’, which has led to a two decade long discussion on their theory.

Theorists of the 20th century have mostly argues that the brain is the embodied place of cognition, however Clark and Chalmers asserted that we have to accept the ‘parity principle’, which states that “If, as we confront some task, a part of the world functions as a process which were it done in the head, we would have no hesitation in recognizing as part of the cognitive process, then that part of the world is (so we claim) part of the cognitive process”. Refuting the ‘parity principle’ and calling it ‘brain chauvinism’ Clark and Chalmers emphasized that we should let go of this long held prejudice and allow the notion of ‘extended cognition’ come more naturally to us.

Clark and Chalmers not only argue that cognitive function can extend beyond the confines of one’s own brain into the environment, but opposed to the views of ‘passive externalism’ featured by Putnam and Burge. In their concept of active externalism, the relevant external features are active, meaning that they have a direct impact on the person then and there, meaning that they influence his or her behaviour and the relevant external features are inside the cognitive loop „not dangling at the other end of long causal chain.” It is not merely that there is a causally active feature in the environment, that influences the brain, but the cognitive process is constituted by this active feature of the environment.

In my presentation I want to briefly summarize the main arguments of Clark and Chalmers’ original essay, in addition I will introduce some counterarguments by theorists who questioned, criticized or were opposed to their concept. Moreover, I will elaborate on the theoretical development of Clark and Chalmers’ concept with regard to its most recent contributions to EMT and examine the question if the acceptance of the extension of cognitive function necessitates the extension of beliefs and intentions as well.

22 November (Wednesday) 5:00 PM  Room 226
Hajnal Andréka
István Németi
 Rényi Institute of Mathematics, Budapest
How different are classical and relativistic spacetimes? 
This is part of an ongoing joint research with Madarász, J. and Székely, G. This research was inspired by László E. Szabó's paper [S]. 

We take classical (Newtonian, or pre-relativistic) spacetime to be the geometry determined by the Galilean transformations. In more detail: Let the universe of the structure CST be four-dimensional real space R4 together with the binary relation of simultaneity, ternary relation of collinearity, and quaternary relation of orthogonality, where four points are said to be orthogonal iff they are distinct and the first two points and the other two points are pairwise simultaneous and they determine orthogonal lines in the Euclidean sense. Let CST represent classical spacetime. 

Relativistic spacetime is the geometry determined by the Poincaré transformations. In more detail: The universe of the structure RST is four-dimensional real space R4 and its relations are collinearity and Minkowski-orthogonality (or, equivalently, the only binary relation of light-like separability). Let RST represent special relativistic spacetime. 

The question whether two structures are identical except for renaming of basic notions is a central topic in definability theory of mathematical logic. It is formulated as whether the two structures are definitionally equivalent or not (see e.g., [Ho]). 

Clearly, CST and RST are not definitionally equivalent in the traditional Tarskian sense, since in CST one can define a nontrivial equivalence relation (the simultaneity), while in RST one cannot define any nontrivial equivalence relation on the universe. However, in "modern" definability theory of mathematical logic one can define new universes of entities, too (cf e.g., [H], [M] or [BH]). In this extended modern sense, in RST one can define a new universe with nontrivial equivalence relations on it (e.g., one can define a field isomorphic to R4). In fact, both spacetimes can be faithfully interpreted into the other. In the following, by definitional equivalence we always mean definitional equivalence in the modern sense. Definitional equivalence of two theories is a mathematical notion expressing "identiy of" theories. Two theories are definitionally equivalent iff there is a one-to one and onto correspondence between the defined concepts of the two theories such that this correspondence respects the relation of definability. The same notion is applicable to structures. 

Theorem 1. CST and RST are not definitionally equivalent. 

To prove Theorem 1, it is enough to prove that the automorphism groups (i.e., groups of symmetries) of CST and RST are not isomorphic. The automorphism group of CST is the general inhomogeneous Galilean group, where "inhomogeneous" means that we include translations and "general" means that we include dilations. Analogously, the automorphism group of RST is the general inhomogeneous Lorenz group. The two automorphism groups are not even definitionally equivalent. This follows from the following theorem which seems to be interesting in its own. It sais that the abstract automorphism groups of the two spacetimes contain exactly the same "content" as the geometries themselves, they "do not forget structure". 

Theorem 2.
(i) CST is definitionally equivalent to its automorphism group as well as to the inhomogeneous Galilean group.
(ii) RST is definitionally equivalent to its automorphism group as well as to the inhomogeneous Lorenz group.

Similar investigations can be found, e.g., in [E], [EH] and [P]. 

[BH] Barrett, T. W., Halvorson, H., From geometry to conceptual relativity. PhilSci Archive, 2016.
[E] Ellers, E.W., The Minkowski group. Geometriae Dedicata 15 (1984), 363-375.
[EH] Ellers, E.W., Hahl, H., A homogeneous dexctiption of inhomogeneous Minkowski groups. Geometriae Dedicata 17 (1984), 79-85.
[H] Harnik, V., Model theory vs. categorical logic: two approaches to pretopos completion (a.k.a. Teq). In: Models, logics, and higher-dimensional categories: a tribue to the work of Mihály Makkai. CRM Proceedings and Lecture Notes 53, American Mathematical Society, 2011. pp.79-106.
[Ho] Hodges, W., Model theory. Cambridge University Press, 1993.
[M] Madarász, J., Logic and relativity (in the light of definability theory). PhD Dissertation, ELTE Budapest, 2002. xviii+367pp.
[P] Pambuccian, V., Groups and plane geometry. Studia Logica 81 (2005), 387-398.
[S] Szabó, L. E., Does special relativity theory tell us anything new about space and time? (

29 November (Wednesday) 5:00 PM  Room 226
István Danka and Péter Neuman
Department of Philosophy and History of Science
Budapest University of Technology and Economics

  Are we able to find out new things about Nature with the sole help of thought experiments?
In this paper we make an attempt to construe the epistemological status of scientific thought experiments in general. In other words, we will show that it is not impossible for a scientific thought experiment to generate new knowledge, which we cannot derive form the underlying theory using logical methods. Our assessment can be viewed as a refutation of John D. Norton’s widely quoted claim that thought experiments are “epistemologically unremarkable”. Our treatment uses a special type of thought experiment as counter-example to Norton’s claim. This is the Monte Carlo simulation based method as used in elementary particle theory. We will argue that this type of simulation provides knowledge about Nature that could not have been derived solely from the underlying exact theory. Monte Carlo simulation is a powerful simulation tool, used extensively in different fields of science, e.g. meteorology, economics, physics, mathematics, etc. For the sake of logical completeness, we will first show that the kind of simulation based methods can and should be categorised as thought experiments.

Modern particle physics heavily relies on the relativistic quantum theory of fields. It is known that this theory, while being extremely successful both in predicting experimental results and accuracy, suffers from serious ambiguities and mathematical inconsistencies. Perfectly legitimate physical questions sometimes get completely unphysical, false answers. By using the machinery of quantum field theory, we may get infinite results for quantities that intuitively and experimentally cannot be infinite. It is a great achievement of 20th century theoretical particle physics to get rid of these infinities, although the solution leaves certain questions open, and it is far from being mathematically (even physically) rigorous and complete. One way of getting rid of the harmful infinities is to define the theory on a discrete lattice (instead of the continuous space-time) and by performing numerical calculations on this lattice we attempt to infer the behaviour of the continuous world. Lattice field theory (with or without computer simulation) is able to provide results that are in certain cases absolutely remarkable because of their unprecedented accuracy, and sometimes otherwise unattainable ontological conclusions. Kenneth Wilson’s 1974 pseudo-proof of quark confinement using lattice treatment is one example of this, but we can also consider the recent result of determining hadron masses using Monte Carlo methods. We will explain that none of the above results can be reached just by relying on the underlying continuous field theory. Moreover, the methods used here are not simply numerical approximations within the paradigm of the theory.

We shall argue, that deriving finite results from infinite ones, cannot be exclusively inferential, especially if we want to avoid the classical problem of induction. However, it seems that computer simulations viewed as thought experiments cannot grant empirical knowledge without relying on empirical observations, provided we clearly understand what we are in the process of studying. Although, Norton’s claim is not tenable, its naive denial will not bring us any closer to the solution.

We will show, however, that the empirical vs. inferential distinction is a false dilemma. The assessment is based on Kant’s view about the existence of predicates providing new knowledge, that are not empirical. The tenet of the synthetic a priori judgements has its impacts on the understanding of thought experiments. We shall reconstruct these impacts in both historical and theoretical contexts. Following Hintikka’s Kant approach we shall interpret Kant using the terminology of possible worlds. We will see that Kant’s synthetic a priori judgements provide non-empirical fresh knowledge, because the thought experiments establish different possible worlds, in which the laws of physics are valid. If these worlds are “close enough” to each other, the method will provide valuable and fresh knowledge about our world, too. The treatment will thus extend our knowledge about Nature.

It can be deemed problematic though from a historical point of view, that Kant himself did not study thought experiments. On the other hand, one of his contemporaries, the physicist Hans Christian Ørsted established the base of a Kantian theory of thought experiments already in 1802. His ideas stayed practically unnoticed, he had no followers most probably because he did not make any distinction between physical and mathematical thought experiments, neither did he distinguish a priori and empirical judgements. Defending Ørsted’s results, we shall show that his Kant interpretation is not only completely proper, following Kant’s traditions, but it is also at least partially tenable for modern thought experiments, as well. Ørsted’s original problem was the question of the infinitesimal. He studied the validity of the knowledge via inferences gained through convergences within the framework of calculus. This problem is analogous to the problem we encounter in the case of Monte Carlo simulation. This is not a surprise, however, we shall make ti clear that the analogy is not perfect.