1The principle of sufficient reason, explicitly formulated for the first time by Leibniz, postulates that all facts have an explanation.

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Caption: Gottfried Wilhelm Leibniz (1646-1716) © DR

2As such, it can pass for a principle of intelligibility of good practice which, according to Leibniz, constitutes one of the two cornerstones of reasoning with non-contradiction. But his radical interpretation, which sees a necessary and unlimited truth in the principle’s extension (not only including the ­current world but also possible ones), is both the most interesting and the most controversial, because of requirements that are perhaps excessive. For the consequences are serious, from the principle of identity of the indiscernible, to the existence of an auto-necessitated being, to the principle of plenitude and the principle of the best. Hence, the challenge of circum­scribing the principle of sufficient reason: is it limited to contingent truths or does it also require reasons from the necessary propositions? If the latter have a sufficient reason, does that mean their truth relies on such reasons? And how can one distinguish, in the order of the explanation, between reasons and causes?

3Far from any overly optimistic rationalism, it became clear ­during this workshop that the contemporary take on the principle of sufficient reason highlights above all its fecundity, both in metaphysics and in epistemology. In this respect, Jean-Baptiste Rauzy (Paris-IV) argued for an ontological reading of this principle, by showing that the nature of ideas must be understood with the concept of expression, which induces a dangerous circularity between expression and knowledge. Jean-Pascal Anfray (école normale supérieure) then showed how the principle of sufficient reason constitutes the cornerstone of Leibnizian spatial relationism: if space were absolute, its material points would be indiscernible, but would each occupy a different position according to an arbitrary distribution, devoid of reason. Jean-Matthias Fleury (Collège de France, 2009-2011), stressed that the principle of sufficient reason also, and perhaps firstly, raises questions pertaining to free will and to the possibilities opened up by human actions, and that it plays a nodal role in the counterfactual analysis of history. Jean-Marie Chevalier (Collège de France) presented the critique of the principle of sufficient reason by a very Leibnizian Charles S. Peirce who, in the Kantian tradition, never­theless opposes the possibility of total intelligibility with the resistance of hard facts. Finally, a series of crucial distinctions were made by Jacques Bouveresse. He dedicated the last two years of his lectures at the Collège de France (2009 and 2010) to the Hanover philosopher, and an electronic publication of the full text of the lectures is now available in the series “The Philosophy of Knowledge at the Collège de France”, under the title Dans le labyrinthe : nécessité, contin­gence et liberté chez Leibniz (In the Labyrinth: Necessity, Contingency and Freedom in Leibniz’s Work). After showing just how unsatisfactory Popper’s critique of the principle of sufficient reason is, Bouveresse pointed out that while this principle does posit that all facts have an explanation, it does not posit that this explanation is accessible, in other words that from the principium rationis to the principium reddendae rationis the consequence is not right – an erroneous inference that invalidates the Heideggerian interpretation. Reason is gaining ground!

The speakers present were:

• Jean-Matthias Fleury (Lycée Louis-Armand in Nogent-sur-Marne & Collège de France). Could Caesar have not Crossed the Rubicon? Leibniz and Reason in History

• Jean-Baptiste Rauzy (Université Paris IV). Leibniz and Armstrong: Having a Good Reason

• Jean-Pascal Anfray (école normale supérieure). Could Space Be Absolute? Sufficient Reason and Identity of Indiscernibles in the Controversy with Clarke

• Jean-Marie Chevalier (Collège de France). Leibniz, Reader of Pierce: the Reasons for the A-Priori

• Jacques Bouveresse (Collège de France). Some Remarks on the Relationships between the “Principle of Contradiction”, the “Principle of Reason”, and the “Principle of the Best” in Leibniz’s Work