Conference celebrating the centenary of the death of Jean Nicod

Monday 18 & Tuesday 19, November 2024

The Jean Nicod Institute commemorates the centenary of the death of Jean Nicod (1893-1924), a French philosopher and logician best known for his contributions to logic and epistemology. With his two major works on geometry applied to the sensible world and on induction (La géométrie dans le monde sensible et Le problème logique de l’induction, both published in 1923), Jean Nicod anticipated central philosophical debates of the second half of the 20 th century. Author of two doctoral theses, including one with Bertrand Russell at the University of Cambridge, he was a bridge-builder between the French philosophical tradition and Anglo-Saxon analytic philosophy.

The conference brings together philosophers, psychologists, social scientists and logicians who have been influenced in one way or another by Jean Nicod’s work.

PROGRAMME

Monday, November 18

10:00 - 10:15 Introduction

10:15 - 11:15 Sébastien Gandon (Université Clermont Auvergne), "Nicod contre Bergson. La structure de La géométrie dans le monde sensible"

11:15 - 11:30 Break

11:30 - 12:30 Fabrice Correia (Université de Genève), "Endurer par procuration"

Lunch

14:15 - 15:15 Francesca Poggiolesi (Institut d’histoire et de philosophie des sciences et des techniques - CNRS) ‘’Explaining with reasons : from Aristotle to Machine Learning Classifiers.” Joint work with Brian Hill (Groupement de Recherche et d’Etudes en Gestion à HEC)

15:15 - 15:30 Break

15:30 - 16:30 Laura Fontanella (Université Paris-Est Créteil) "Chicken or egg ? Axioms or models ? Who comes first ? Jean Nicod on geometry, and the role of axioms in mathematics"

16:30 - 17:30 Kevin Mulligan (Università della Svizzera italiana), "La Phénoménologie de la Perception de Jean Nicod"

17:30 - 19:30 Cocktail

 

Tuesday, November 19

10:00 - 11:00 Pascal Engel (Centre de Recherches sur les Arts et le Language-EHESS), “Nicod, la barre de Sheffer et la logique du jugement”

11:00 - 11:10 Break

11:10 - 11:40 Mariana Babo Rebelo (École Polytechnique Fédérale de Lausanne, Instituto de Investigaciones Biomédicas August Pi i Sunyer, “A grid-like code for two-dimensional perception of passive skin touch”

11:40 - 12:40 Patrick Haggard (University College de Londres), “Hopping, stroking, sensing, knowing : sensorimotricité et espace chez Nicod”

 

ABSTRACTS

Sébastien Gandon (UCA)

"Nicod contre Bergson. La structure de La géométrie dans le monde sensible"

L’intervention vise à expliquer comment Nicod, en "inversant" la méthode des constructions logiques russellienne, parvient, dans La géométrie dans le monde sensible, à répondre à la thèse bergsonienne selon laquelle spatialiser l’expérience, c’est la trahir.

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Fabrice Correia (UniGe)

"Endurer par procuration"

David Lewis a proposé une formulation de la distinction entre endurance et perdurance – deux manières antagonistes d’exister dans le temps – qui est rapidement devenue canonique : une entité perdure si elle possède une partie temporelle à chaque moment de son existence ; une entité endure si, au contraire, elle est « complètement présente » à chaque instant de son existence. Si la caractérisation de la perdurance est relativement claire, celle de l’endurance a été considérée par de nombreux philosophes comme étant mystérieuse, à juste titre : que veut dire « être complètement présent à un instant » ? Suite aux travaux importants de Josh Parsons sur le concept de localisation, Cody Gilmore a proposé une caractérisation « locationnelle » de l’endurance qui est aujourd’hui largement acceptée. Cette caractérisation est sur la bonne voie, mais elle exclut certains scénarios qui sont conceptuellement possibles, et manque pour cette raison de généralité. En m’appuyant sur une nouvelle théorie générale de la localisation, ainsi que sur une idée importante mise en avant indépendamment par Jean Nicod et Theodore de Laguna, je proposerai une caractérisation de l’endurance qui échappe au problème rencontré par celle de Gilmore.

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Francesca Poggiolesi (CNRS-IHPST)

"Explaining with reasons : from Aristotle to Machine Learning Classifiers"

joint work with Brian Hill (GREGHEC)

Explanations, and in particular explanations which provide the reasons why their conclusion is true, are a central object in a range of fields. On the other hand, there is a long and illustrious philosophical tradition, which starts from Aristotle, and passes through scholars as Leibniz, Bolzano and Frege, that give pride to this type of explanations, and is rich with brilliant and profound intuitions. Recently, Poggiolesi (2024) has formalized ideas coming from this tradition using the logical tools proper to proof theory. On the one hand, recent work has focused on Boolean circuits that compile some common machine learning classifiers and have the same input-output behavior. In this framework, Darwiche and Hirth (2023) have proposed a theory for unveiling the reasons behind the decisions made by Boolean classifiers, and they have studied their theoretical implications. In this talk we will show the deep links behind these two trends : in particular, we will demonstrate that the proof-theoretic tools introduced by Poggiolesi can be used to compute the complete reasons behind the decisions made by Boolean classifiers and we will illustrate them using examples.

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Laura Fontanella (UPEC)

"Chicken or egg ? Axioms or models ? Who comes first ? Jean Nicod on geometry, and the role of axioms in mathematics"

In the late 19th century, the discovery of non-Euclidean geometries profoundly challenged the foundations of mathematics, particularly the role and nature of axioms. This period raised essential questions : do axioms express fundamental truths, intuitions, or are they simply definitions whose validity rests solely on logical consistency ? Geometry became the arena for this debate, but at stake was also the legitimacy of Hilbert’s axiomatic program for all of mathematics and the nature of axioms remains a central question today in all areas of mathematics, particularly in set theory.
In his doctoral thesis, La géométrie dans le monde sensible, Jean Nicod provides an insightful and original analysis of how geometry—or rather, geometries—emerge from perception. The traditional approach to axiomatic systems is then reversed, axioms are not the starting point but the result of a process of abstraction from data perception. We will examine Nicod’s conception of axioms emerging from his analysis and discuss the extent to which this perspective on axioms might be extended to other areas, such as arithmetic and set theory.

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Kevin Mulligan (USI)

"La Phénoménologie de la Perception de Jean Nicod"

Le projet de décrire exactement ce que nous voyons soulève tôt ou tard la question du rôle des propriétés et des relations formelles – telles que la propriété d’être un tout, les relations de dépendance, de partie-tout, d’occupation ou de localisation spatiale - dans ce que nous voyons et dans sa description. Je présente et évalue quelques réponses allemandes, anglaises, autrichiennes et françaises à cette question, notamment celle de Jean Nicod.

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Pascal Engel (EHESS-CRAL)

"Nicod, la barre de Sheffer et la logique du jugement"

En 1916 Jean Nicod montre que les propositions primitives des Principia de Russell peuvent toutes être exprimées par un seul axiome au moyen de la barre de Sheffer (NAND : pas à la fois A et B)
p | .q | r : | ::s | .s | s : | ∴ s | q. | :p | s. | .p | s

Ce résultat avait été anticipé par Peirce, mais Nicod est le premier à en donner la démonstration. Dans cet exposé je voudrais en considérer quelques conséquences en philosophie de la logique. 1) Du point de vue de ce que l’on appelait alors la « logique du jugement ». Dans deux articles, l’un portant sur le Traité de logique de Goblot (1918), l’autre sur la relation de la forme et du sens (1924), il s’oppose au psychologisme de ce dernier au nom de la « logistique ». Une question que ne soulève pas explicitement Nicod, mais qui joue un rôle important chez Reinach (1911) à la même époque, et un peu plus tard chez Ramsey, est celle de savoir si la négation doit être interprétée comme un acte de rejet d’une proposition. La barre de Sheffer ne permet pas d’exprimer ce sens, qui a été récemment remis à l’honneur par Rumfit (2000, voir Mulligan 2013). 2) On a pu montrer que la barre de Sheffer peut être envisagée non pas à partir du style axiomatique de Nicod-Russell, mais du point de vue du calcul des séquents. Dans quelle mesure cela permet-il d’exprimer p | q et la conception inférentialiste des constantes logiques ? 3) Une autre conséquence du résultat de Nicod a été tirée par Wittgenstein dans le Tractatus, où il est affirmé (6. 001) que toute proposition authentique est constructible à partir de propositions élémentaires à partir d’une unique fonction de vérité N, qui généralise la barre de Sheffer. On s’est demandé si cela valait pour toute proposition, y compris pour la logique de la quantification.

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Mariana Babo Rebelo (EPFL, IDIBAPS)

"A grid-like code for two-dimensional perception of passive skin touch"

The skin is the envelope of the self. As a 2-dimensional system, it has interesting analogies with external, environmental, space. Both contain landmarks and boundaries, and both can be navigated. Here we tested whether neural mechanisms known to encode trajectories in environmental space, i.e. grid-cells, also encode the location of a stimulus travelling across the skin in a similar way.
In this fMRI study, the experimenter drew line segments across the participant’s hand dorsum (n=29). BOLD activity did not show the typical signature of grid-cells (Doeller et al 2008) when testing a regular tactile space. However, given that tactile receptive fields are oval-shaped and that, as a result, tactile distance perception is anisotropically distorted (Longo & Haggard 2011), we further hypothesized that a grid representation of the skin might display the same distortions. When we distorted the tactile space based on tactile anisotropy (i.e. shrunken lateral axis), we did find grid-cell like representations in the entorhinal and somatosensory cortices, indicating the presence of a grid code that reflects sensory input physiology.
Similar cognitive mechanisms are thus used for encoding the positions of stimuli on the skin, as for navigation in the environment. The two-dimensional sensory surface of the skin constitutes a self-space that supports the full complement of spatial representations, and therefore serves as a ‘tactile field’, analogous to the concept of a visual field. Our results therefore challenge theories that view proprioception, rather than passive touch, as the key necessary condition for spatial self-representation.

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Patrick Haggard (UCL)

"Hopping, stroking, sensing, knowing : sensorimotricité et espace chez Nicod"

Jean Nicod’s work on sensory geometry explores the minimum sensory requirements that a creature needs to have spatial awareness. He makes a broad distinction between perspectival geometries, and geometries that depend on some sensation of movement. The sense of touch is interesting in this respect, because it potentially figures in both approaches. For Nicod (though not for some other philosophers), touch has the properties of a sensory field, analogous to the visual field. This suffices to support the proto-spatial property of inclusion (entre). At the same time, many of Nicod’s thought-experiment examples rely on what Gareth Evans called "travel-based space", i.e., the accumulation of movement sensations that represent a path through an external world. This primacy of movement information in spatial awareness has its neuroscientific roots in the work of Helmholtz, and is logically equivalent to the Lotze/Wundt concept of ’lokalzeichen’. Its most recent manifestation is the neuroscientific work on place and grid cells recently recognised by the Nobel Prize awarded to John O’Keefe, May-Britt Moser and Edvard Moser

Discussions of the importance of movement for spatial perception, and indeed of full-blooded self-consciousness, often use self-touch as an example. The spatial percept that the mosquito is biting me just there on my left hand may be linked to the motor command that my brain sends to my right arm to try to squash the mosquito, or to scratch the resulting itch. The spatial properties of touch, such as location, distance etc., thus depend ultimately on the movement information required to target those locations. This idea appears never to have been tested experimentally, despite its long history. I will discuss a series of experiments in which two haptic robots in a leader:follower configuration allow the experimenter to intervene in the normally-direct relation between movement and touch, and thus investigate whether spatial perceptions of distance are dominated by efferent motor signals, or by afferent tactile signals. Our experiments found little support for the traditional view of motor dominance of space perception. Rather we found that tactile input can influence the spatial perception of movement, sometimes by just as much as movement can influence the spatial perception of touch. I will argue that the primacy of motor information in spatial awareness may be oversold - at least for the case of self-touch. The tactile sensory field of the skin, coupled with the temporal succession of stimulus events, may itself play an important foundational role in spatial awareness. I will speculate that the co-emergence and co-construction of sensory fields and widening motor repertoires during early development could enable a form of self-supervised learning that leads to spatial awareness of both one’s own body and the external world.

 

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