FRAL - Programme franco-allemand en SHS

Jurisprudence and Logic – Jurilog


Jurisprudence and Logic

Legal Reasoning and Logical Reasoning

Along the History of Philosophy we can recognize a recurrent question concerning the relations between logic and law, namely respecting a possible mode of reasoning specific to Law. Although in the core of these two disciplines we identify different aspects which are even independent and autonomous, no jurist would ever say that he reasons “illogically”, in the same way that no logician would deny his having to logically and methodically obey and apply certain laws. This shows that these two disciplines, despite their differences, still share some common interests and are placed together in the problematic concerning logical reasoning.

Even if legal and logical reasoning share some similar background aspects, they do however differ in the practical usage of the reasoning modes which are performed. Consequently, logic in its formal or “calculator” aspect does not seem to fit the necessity of apprehending the practical features of legal reasoning.

For our project, we have chosen the dialogical logic approach, which comes from the tradition started by Lorenz and Lorenzen (Erlangen, Germany) and allows apprehending logic not as simple calculus, but as an argumentative practice. Contrarily to other approaches, the argumentative approach of logic offers a frame of study where it is allowed to combine different kinds of logic, but also to change them thanks to an argumentative practice based on a set of logical rules. Because of our methodological tools, we are then capable to explore the legal reasoning field by the perspective of an argumentative practice.

In order to achieve our objectives, we have put together in our team not only researchers in Law, but also in legal History and in logic. While Lille’s research team is mostly dedicated to the development of a logical-philosophical frame allowing formalizing the usage of argumentative practices in dialogs, the Konstanz’s research team offers the expertise not only in Law but also in legal History. Our work takes as a point of departure the logical/legal writings of Leibniz about the notion of condition – a notion designed by him as being mutual to both logical and legal domains. In the beginning, we study and measure the influence that Roman law had over the development of Leibniz’ works concerning the conditions, in the same time that we consider the contemporary pertinence of those reflections and the results reached by this author.

Roman law tradition approaches the problematic of legal conditions from the dimension of the objective existence. We have managed to put into evidence the fact that Leibniz’ approach is centered in the epistemic subject. The focus on the importance of the dynamic epistemic dimension, advocated by Leibniz in his legal theory of condition, is a remarkable result, which allows us to engage in the contemporary debate about the epistemic character of the suspensive condition in French Law. This problem is in the core of a current proposition of revision of the Article 1181 of the French Civil Code, via the Catala Project 2005 and another project of law from 2011.

Furthermore, the constructivist type theory approach, once developed in the dialogical frame, has already allowed the formal reconstruction of the notion of suspensive condition. According to this approach, the relation between condition and conditioned is understood as the result of a dependency relation among sets of proofs. This particular relation among sets of proofs allows us to establish a strong link between the notions of proof and presumption, as well as to overcome the obstacles disregarded by the previous approaches – namely those related to the classical problems concerning logical conditional structures (trivialization of the relation by the satisfaction of the consequent or the falsification of the consequent).

Concerning the publications, many papers have already been submitted and are by the moment under review: “Fiction in Legal Science: the Strange Case of the Basic Norm” In: Proceedings of ISELL, Springer, “The definition of Legal Norm (from a philosophical point of view)” and “Condition, Between Law and Logic” In: Proceedings of the 6th Annual Legal Research Network Conference, Springer, respectively by J.M. Sievers and S. Magnier. The monograph “Epistemic Dynamics, Dialogs and Legal Reasoning”, LAR, Springer, by S. Magnier is in course of redaction. Two collective works: “Norms and Conditionals”, M. Armgardt, S. Rahman & A. Thiercelin. (Eds.) and “From Dialogue to Dialogue”, by S. Rahman and N. Clerbout are also currently in production.

Concerning the upcoming researches at the center of our concerns, a research between lawyers and logicians on the influence of Leibniz on the French Civil Code must be deepened. The results will allow us to investigate the relevance of Leibniz's epistemic argument in the French contemporary law. This reflection is essential in the contemporary debate about the rewriting of some articles of the French Civil Code. If we can show the need for epistemic dimension of the suspensive condition in the contemporary law, the logical reconstruction of Leibniz's theory could be applied to contemporary legal issues. Another major task about the constructivist type theory will further explored. The results could establish a link between the proof theory and the notion of presumption.

Collective books :

Legal Reasoning and Logic. Past and Present Interactions, M. Armgardt, P. Canivez & S. Chassagnard-Pinet (Eds.), sous presse.

Individual books :

Sébastien Magnier, Approche dialogique de la dynamique épistémique et de la condition juridique, Cahiers de logique et d’épistémologie, College Publications, London, 2013.

Papers in journal :

Shahid Rahman, Nicolas Clerbout, Zoe McConaughey « On play-objects in dialogical games. Towards a Dialogical approach to Constructive Type Theory », Tributes for Jean Paul van Bendegem, P. Allo (Ed.), College Publications, London, sous presse.

Shahid Rahman, « Constructive Type Theory and The Dialogical Turn. A New Start for the Erlanger Konstruktivismus », Paderborn: Mentis in Dialogische Logik, Mittelstrass (Ed.), sous presse.

Matthias Armgardt, « Salvius Iulianus als Meister der stoischen Logik – zur Deutung von Iulian D. 34,5,13(14),2-3 », in Matthias Armgardt, Fabian Klinck, Ingo Reichard : Liber amicorum hristoph Krampe zum 70. Geburtstag, Freiburger Rechtsgeschichtliche Abhandlungen Bd. 68, Berlin 2013, S. 29-36, 2013.

Sébastien Magnier, Tiago de Lima, « A Soundness and Completeness Proof on Dialogs and Dynamic Epistemic Logic », in Dynamics in Logic, special issue of Logique et Analyse, P. Allo, F. Poggiolesi and S. Smets (Eds.), sous presse.

“The notion of condition in Law takes place in different settings, in different times. The particularities of each one of these conditions involve different consequences. These consequences have rather real influences, even if the conditions can be fictive themselves. While conditions constitute a central theme for jurisprudence, the multiplicity of the notion of condition represents also a central theme for the History of Logic. Nevertheless, it is well known that the jurisprudential perspective and the philosophical perspective do not blend naturally, without any problem. It is due to this fact that the present project takes as a mission the study of the tensions in the relations between Law and Logic, and this study will be accomplished according to three particularly significant contexts: the ancient Roman period, G. W. Leibniz, and the contemporary Law. The main objective of the project is the coordination of the juridical and logical aspects of the notion of condition, in order to promote in a decisive manner the constitution of a universal juridical logic. The three periods already mentionned are historically relevant, each one for their own reasons, and they will represent our three main research points. They constitute a connection between logical and juridical approach of the notion of condition, and they manifest through the History the conscience of a special problematic, which raises many discussions in the contemporary research. It is evident by the description that we have rendered that the problematic of our project concerns the writings of Leibniz and, according to our approach, we also suggest that the framework of the dialogical logic, which nowadays reaches significant improvements, represents a promising background for the philosophical interpretation of it. Thus, we expect to open new perspectives in the study of the challenge of the interface between juridical representation and logical modeling in each one of the three researching points mentioned above, but also in a transversal manner across them.”

Project coordination


The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.


Universität Konstanz Universität Konstanz

Help of the ANR 210,000 euros
Beginning and duration of the scientific project: March 2012 - 36 Months

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