Jean Cavaillès, the philosopher and explosives expert
- David Moreno
- 5 days ago
- 5 min read
Updated: 3 days ago
In his essay *Courts-circuits *, published in April 2023, Étienne Klein devotes a fascinating chapter to Jean Cavaillès. We discover an innovative philosopher-mathematician, a Resistance network leader endowed with terrifying courage… The Germans executed him in the citadel of Arras on April 4, 1944.
Let's state it from the outset: what makes Jean Cavaillès unique is his ability to combine the most abstract intellect with total commitment to perilous missions. For a brilliant graduate of the École Normale Supérieure who, in the late 1930s, began to revolutionize the foundations of philosophy, the temptation to isolate himself in an ivory tower could have been great…
…But the comfortable life of an established intellectual didn't suit him, especially when the Nazis invaded half the country. Cavaillès, with his comrades-in-arms, then launched into frenzied acts of sabotage, targeting trains, factories, and other strategic infrastructure … As if to ward off bad luck, he liked to boldly repeat to his troops: “ Where there is danger, there too must be the leader; it's so much fun .”
Betrayed by a member of his network, he was arrested on August 28, 1943, by agents of the Leopold Service, the Parisian branch of Nazi counter-espionage. Interrogated and tortured repeatedly, he revealed no names. After several months of imprisonment, he was sentenced to death for his " large-scale activities against the occupying forces ." He was executed by the German army the day after his verdict.
The filmmaker Jean-Pierre Melville, himself a former member of the French Resistance, pays fervent homage to the philosopher and mathematician in his masterpiece *Army of Shadows * (1969), adapted from the eponymous novel by Joseph Kessel (1943). Melville drew inspiration from Cavaillès for the character of Luc Jardie, the network leader played by Paul Meurisse. In the film, Melville includes two of Cavaillès's books, whose titles are clearly visible on screen: * Transfinite and Continuous * and * Axiomatic Method and Formalism *.
A deep-seated attachment to freedom of thought and action
From a young age, our man displayed a fierce independence of mind and an extraordinary fighting spirit. At just 19, he gave striking proof of this… Undeterred by failing the entrance exam for the École Normale Supérieure in 1923, he showed remarkable resilience the following year. Rebelling against the rigid and dogmatic teaching of the preparatory classes, he skipped classes at the Lycée Louis-le-Grand to prepare for the exam on his own. Against all odds, he achieved first place in the "Latin-Science" category.
Despite the loneliness of his first months at the École Normale Supérieure, Jean Cavaillès formed a close friendship with Georges Canguilhem. Canguilhem would also become a prominent figure in the French Resistance during World War II. Upon the establishment of the Vichy government, Canguilhem resigned from his teaching position at the Lycée Fermat in Toulouse, explaining to the Rector of the Academy that he had not passed the agrégation examination in philosophy to teach "Work, Family, Fatherland. "
Cavaillès pursued studies in both philosophy and mathematics. A well-rounded individual, he also enjoyed physical exercise and the outdoors. A passionate mountaineer, he spent every summer climbing the rocky faces of the Pic du Midi with his equally intrepid cousins, who were also avid mountaineers. " For [according to Cavaillès] the body and nature count as much as the intellect ," wrote Étienne Klein in Courts-circuits . He earned his agrégation in philosophy in 1927.
Another striking characteristic was his profound anti-racism, which he courageously demonstrated on two occasions in his life. The first was in 1928, during his military service as a second lieutenant; he insisted on fulfilling his duty within a unit of Senegalese riflemen, in homage to their exemplary contribution during the First World War. The second was when he was taken prisoner at the Cambrai citadel in June 1940; he persisted in protesting against the public humiliations inflicted upon Black soldiers, despite threats of execution from his captors.
Having long been influenced by Catholicism (while being Protestant), he finally opted for Spinozism. In the early 1930s, Jean Cavaillès believed that ethics could do without religion, provided it became a humanism based on sound reasoning and coherent principles, a kind of "theory of reason".
By extension, philosophy according to Cavaillès should follow the model of mathematical construction (axiomatic and conceptual description of the world) more closely than that of literature (subjective and metaphorical description of life). He aims to weave a new philosophy like a mathematical theory with its definitions and axioms, its theorems and lemmas.
Germanophile and perfectly bilingual, Cavaillès was stunned by reading Mein Kampf in 1934, which he considered a deplorable hoax, full of absurd theories, senseless prejudices, and rampant anti-Semitism.
Cavaillès, the embodiment of integrity and courage
Taken prisoner during the French defeat as a cipher officer, Cavaillès was not one to remain imprisoned for long: he escaped in July 1940 during his transfer from Cambrai to a prisoner-of-war camp in Germany. Crossing Belgium by bicycle, he hid for a few days in Lille. Using false papers, he reached Clermont-Ferrand, which had become a refuge in the unoccupied zone.
Jean Cavaillès taught logic at the University of Strasbourg, which had relocated to Clermont-Ferrand. This position provided him with ideal cover for his clandestine activities: with Lucie Aubrac and Emmanuel d'Astier de la Vigerie, he co-founded the Libération-Sud resistance movement. Here are Étienne Klein's words to describe Cavaillès's striking beginnings in the Resistance:
His considerable charisma captivated everyone he met. It must be said that Jean Cavaillès proved capable of multitasking: preparing a lecture, writing a scholarly article, recruiting agents, meticulously planning an act of sabotage, and developing a new encryption system. For him, thinking and acting were one and the same […] Lucie Aubrac would later express her admiration for “all the power of mind, hope, and will that emanated from him.”
Despite his rank as network leader, he loves nothing more than being in the field, in contact with his comrades. He readily undertakes perilous missions, especially when it comes to blowing up logistical installations used by the enemy: railways, heavy equipment depots, transformers and power lines, etc.
Nicknamed "the sabotage expert" for his skills in using explosives like TNT and retardant devices, Cavaillès went completely underground in 1943. From then on, he traveled with a multitude of false papers, complicating matters for German intelligence services… It was only natural that in June of the same year, he founded the Cohors intelligence network, an action group dedicated to training saboteurs.
Early summer 1943. Disguised as a naval mechanic, Jean Cavaillès infiltrates the German submarine base at Lorient alone, right under the noses of hundreds of German soldiers and officers. His goal: to gather as much information as possible to provide to the Allies.
Another distinctive feature… According to his comrades and friends, Cavaillès's involvement in the Resistance was less an act of rebellion against the Nazi occupiers than an action consistent with his worldview. Here again, we see the influence of Spinoza. Indeed, as early as 1931, he wrote: “ We are led in everything. Led, but not constrained or forced, led as if by light. ” More than a moral or political obligation, the Resistance stemmed from logic: the situation was unacceptable; there was no other choice but to resist.
Today, in 2025, the intellectual and ethical integrity shown by Jean Cavaillès is invaluable to those who, in their own way, aspire to fight the fascization of minds in France and USA.
This text is the result of an automated translation. The first version of this text (in French) is available at the following address:
Sources :
Étienne Klein, Courts-circuits, éd. Gallimard, 2023, 224 pages. « La morale d’acier de Jean Cavaillès »
Jean Cavaillès – Wikipedia
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