Kant in the underground: the Enlightenment, vegetarianism, and anti-Nazi resistance

This article explores the little-known history of the ISK, an anti-Nazi resistance movement that combined enlightenment philosophy with ethical socialism and a commitment to, among other things, anti-democratic politics, sobriety, and vegetarianism. What can the organisation tell us today about life lived in service to a political cause?

During his imprisonment for anti-Nazi activities, the Munich grocery store owner Ludwig Linsert found fortitude in the imprecisely remembered writings of Immanuel Kant. Steeling himself to face Gestapo interrogations, Linsert grasped for a line from Kant’s Metaphysics of Morals: ‘For if justice goes, there is no longer any value in human beings.’¹ Decades later, Linsert recalled how this idea encouraged him to remain confident that, despite many sacrifices, resistance gave a ‘deeper meaning’ and an ‘ethical content’ to his life and the lives of his comrades.²

Equally as vivid to Linsert, in his gestapo cell, was a song from his days in a social democratic youth movement. During his months of pre-trial detention, which included more than a year spent in the boiler room of a Bavarian prison, he was accompanied by the lyrics and rhythm of the folk song Die Gedanken sind Frei, ‘Thoughts are Free.’ Hitler, Linsert remembered, promised heads would roll. And yet Linsert could still think with his head. His thoughts about Kantian ethics, resistance, the fate of his friends and family, and the future of Germany – all remained free.

Ludwig Linsert’s musical tastes and philosophical predilections reflected his membership of a largely forgotten anti-Nazi movement: the Internationaler Sozialistischer Kampfbund or International Socialist Struggle League. Formed by a neo-Kantian philosopher in the mid-1920s, the ISK found its most valuable recruits among the vibrant political youth culture of Weimar Germany. The organisation’s name was pronounced by its members as a single sharp word: ISK as in Risk. The full title reflected an unrealised objective: global reach (the movement was chiefly made up of Germans, a scattering of Brits, some Chinese students and, briefly, a man from County Donegal) along with more grounded aspirations: a philosophical commitment and a militant spirit.

For a movement whose number never exceeded more than a few hundred, the ISK enjoy vast archives. Their memoir literature is prolific; the surveillance and police investigation folders on their activities bulge. A valuable, if dated, German-language literature contains detailed insights into the organisation’s ideas, membership and activities.³ Yet beyond a small world of social democracy history obsessives, the ISK are remembered today, if they are remembered at all, as a kooky sect that combined dietary advice from the man who invented muesli with an anti-democratic political programme.⁴ The historian Su Lin Lewis recently summarised scholarly opinion of the ISK and its contributions: ‘An eccentric cult of German emigres’.⁵ But, as Lewis’ work suggests, to dismiss those whose political lives were shaped by the ISK as cultish automatons is to  abandon insights their unusual political path presents.⁶ The organisation offers historians an unusually well-documented laboratory to test what it means to live wholly for an idea. If we live in a society governed by the ignoble and malevolent, how do we remain steadfast in our commitment to our principles? 

Ludwig Linsert, who found himself humming Die Gedanken sind Frei between Gestapo interrogations, knew much about the joys and costs of devoting one’s life to an idea. Alongside his wife Margot, Ludwig ran ‘Lebensmittel Linsert’, a grocery store on Munich’s Fürstenrieder Strasse. The store was connected to the ISK’s wider network, which consisted of four vegetarian restaurants – one each in Berlin, Frankfurt, Hamburg and Cologne – and a bread delivery service in Hannover. The network also maintained three European satellites, all vegetarian restaurants: one in Paris, one in Amsterdam and another in London. 

Kitchens provided activists with financial and nutritional sustenance; restaurants premises provided cover for resistance organising. It was not until 1938, after a years-long operation, that the Nazis finally quashed the ISK’s German operations. Yet those restaurants beyond their jurisdiction continued to thrive. The outbreak of war led to many of the exiled chefs, cooks, managers and staff being interned as ‘enemy aliens’. The tenacious ISK members eventually emerged from behind wired fences to coordinate successfully with Allied military intelligence.

It was this curious concept – an enduring anti-Nazi resistance network that doubled as an organic food enterprise – that drew me to the ISK. While writing my first book, a history of communism told through the lens of Moscow’s Hotel Lux in the 1920s, I became interested in Edo Fimmen.⁷ A Dutch trade unionist, Fimmen played a commanding role in organised resistance to fascism from the 1920s until his own death in 1942.⁸ Fimmen juggled his political career as general secretary of the powerful International Transport Workers’ Federation (ITF) with his personal commitments to his two separate families: the two adult children of his wife and two young girls born from Fimmen’s romance with the German socialist Emmy Leonhard. I noticed, as the historian Dieter Nelles had already realised, that Fimmen’s network within Germany was built on trusting relationships with a small circle of comrades.⁹ These comrades shared a distrust for communist groups and a frustration with the gradualism of social democrats. Among them were members of the ISK.

Much of the popular memory of anti-Nazi resistance focuses on those groups who arose in response to Nazism – the White Rose student-led movement or the 20 July plotters drawn from the military elite. The ISK represents something different. Here was an organisation that was, in effect, already training for underground life years before Hitler’s rise to prominence. Their founder had already laid out the practices and ideas of the organisation by the time of his death in 1927, a year before the National Socialist German Workers’ Party first registered faintly on Reichstag electoral results. What guided this movement into early resistance? What led them to so selflessly commit themselves to years of underground life? And what compelled them to undertake what was perhaps their most distinctive ideal: a vegetarian diet?

The ISK was founded in 1926 by the philosopher of ethical socialism Leonard Nelson (1882-1927). As an academic at the prestigious University of Göttingen, Nelson belonged to an intellectual set that included the earliest theorists of quantum mechanics. But Nelson saw little value in theories that did not translate to practical action. In April 1917, he launched the International Youth League to inculcate young socialists with his own distinct brand of moral philosophy. Nelson officially formed the ISK when the leadership of the German Social Democratic Party (SPD) expelled his youth league. The official reason for expulsion was ‘cell-building’ within the SPD, but beneath this rationale lay deeper incompatibilities. The ISK’s strident anti-clericalism was antithetical to the coalition-building focus of the SPD right, while the ISK’s rejection of historical materialism in favour of moral philosophy found few supporters on the SPD left.¹⁰

Leonard Nelson’s Kant for animals

For Nelson, who sought to build on the Kantian philosopher Jakob Friedrich Fries (1773-1843), there was an objectively moral way to live that could be uncovered through philosophical enquiry. Such enquiry did not involve solitary concentration or leafing through holy books. Universal moral law must be uncovered in group discussions – what Nelson declared the return of Socratic Dialogue – wherein participants were encouraged to reach the correct moral line. Against Marxism’s pronouncements about the historical inevitability of a more rationally planned society, Nelson argued for a vision of socialism that would emerge victorious only once its adherents proved its moral worthiness through their actions. 

To modern readers this philosophy may seem little more than the overconfident application of enlightenment ideals – yet it allowed Nelson’s followers to enchant themselves with the belief that goodness, if willed, could triumph. Young men and women, searching for a fixed vision of an ethical life in a time of chaos, found Nelson’s ideas appealing. In the words of ISK member Eva Lewinski, who entered Nelson’s circle as a young woman, Nelson’s ideas provided a ‘philosophical foundation for a moral obligation to political activism’.¹¹

Nelson’s innovation on both his Kantian antecedents and the major theorists of socialism was his interest in applying his politics beyond humanity. For Nelson, socialism not only could but must liberate all sentient beings. Kant argued human dignity arises from our ability to impose moral laws upon ourselves; we should therefore act morally towards those possessed of that same dignity.¹² Nelson asked: why stop there? Humans, Nelson argued, have duties that extend to all sentient beings. If we allow that any creature capable of agony has an interest in avoiding pain, rational beings have a duty to respect that fact, even if said creatures experience no reciprocal duties towards humans. To extend ethical behaviour only to other ‘rational’ actors was, Nelson saw, a flawed approach. ‘If we regard fully developed reason as man’s distinctive characteristic’, he argued, ‘we shall obviously have to equate children and the feeble-minded with animals, and sacrifice their lives and interests to the lives of other men.’¹³In a pre-emptive rebuttal of Nazi eugenics, Nelson emphasised that such a position was morally indefensible. 

Nelson was not uncritically beholden to the categorical imperative, Kant’s famous formulation that you should only act in accordance with a maxim that you would, at the same time, will to be a universal law. Behaviour that contradicted conventional understandings of morality, from telling lies to inflicting violence, could be justified when resisting a force that transgressed the rights of many. What every decision required was a rigorous balancing of human rights, the interests of sentient beings, and our duties towards both. As such, to kill animals for food when an opportunity for an alternative diet existed did not strike Nelson as a moral ambiguity. Speaking at a 1942 Conway Hall meeting, Minna Specht, the ISK’s leading theoretical light, described how the membership condition of vegetarianism acted as ‘proof of the stand the organisation takes, that we use the means at our disposal to fight exploitation.’¹⁴ Every meal clarified for members the nature of their commitment. 

If Nelson’s philosophical argument for vegetarianism can seem noble and even prescient, his other demands now appear less readily so. ISK recruits were compelled to renounce Church membership. Followers were prohibited from smoking and consuming alcohol. Party fees were a significant proportion of their tight Weimar salaries. Celibacy was encouraged among leading members, and for those unwilling to live the personal life of a Nelsonian monk or nun, the leader could judge the suitability of a member’s choice of romantic partner. 

But the component of ISK ideology usual cited as its fatal flaw was not its intrusions into its members’ personal lives, but rather the organisation’s opposition to democracy. For Nelson, democracy was wholly incompatible with a just state. This ‘heirloom of the bourgeois ideology’, as he termed it, allowed majorities to impose their will upon a minority. His solution was a form of elite rule wherein the elite in question would be a caste of rigorously trained ‘lovers of justice’, rather than a racial or class elite.¹⁵ This anti-democratic stance dovetailed curiously with ISK anti-clericalism. Nelson openly envied the Catholic Church’s organisational model even as he derided its results. As Nelson saw it, the Vatican used its powerful top-down structure to lead men towards superstition rather than secular philosophical truth. Roman Catholicism therefore came under sustained ISK critique because Nelson believed it deployed the correct methods towards the wrong ends.

Nelson did not side-step the notion that power corrupts, instead arguing democracy itself encourages the self-interested to seek leadership roles. The solution was to train a generation of leaders who would reliably act in an ethical manner. Remember: Nelson was convinced that his own innovation on Kantian ethics offered a method to determine the ethical decision in any given situation. True political justice required a state ruled by a ‘Party of Reason’, i.e., people trained in this method. A Philosopher Papacy answerable to a highly trained College of Socialist Cardinals. What could go wrong? 

Nelson, to his credit, never built his own leadership cult. In part, he was short on time. He died of pneumonia in 1927 at the age of forty-five, only a year into the ISK’s existence. But it was also the case that the emphasis on collective philosophical discussions encouraged individuals to develop their own path towards justifying Nelson’s edicts for themselves. ISK members considered the party an order crafted along consciously agreed rules and not a cult based on blind rituals. 

The best argument against perceiving the ISK as a sect beholden to one power-hungry individual is its persistence after Nelson’s death. Ultimately, the ISK’s ideas, as well as its diet, would face their strongest tests in the years immediately following the founder’s demise. The activists faced real versions of the parlour games favoured by moral philosophers. Should you lie to protect the life of a comrade? Should you forego meat even as a prisoner subject to meagre rations? Does it serve the greater good to kill someone you consider evil?  During the Nazi era, such questions attained true stakes. 

The ISK in the underground

The years following Nelson’s death were shaped by the ISK’s commitment to opposing the electoral rise of the Nazis. This culminated in the ISK’s oft-cited 1932 contribution to a united anti-Nazi front: the Dringender Appell für die Einheit, the ‘Urgent Call for Unity’. An open letter calling on the KPD and SPD to unite as one electoral front, the Urgent Call was signed by a range of intellectual luminaries including Albert Einstein, the artist Kathe Köllwitz and the sociologist Franz Oppenheimer. 

Of course, the ISK’s appeal went unheeded. The SPD and KPD fought the elections as political opponents and 1932 saw the Nazi Party secure the largest vote share for a single party in both the July and November elections. Yet the left still performed well, with a combined left vote of 37 per cent against the Nazi’s 33 per cent in the November election. The KPD and SPD together secured almost a third of the vote even during the March 1933 Reichstag elections, which were conducted under Nazi coercion – a testament to the opportunity that the ISK’s Urgent Call had sought to realise. More than the cold consolation of retrospective correctness, this voting pattern suggested to the anti-Nazi resistance the existence of a population – cowed but evident – that could be drawn into action against the regime.

Shortly after Hitler took power, the ISK was declared staatsfeindlichen, hostile to the Nazi state, and its activities ruled illegal. In March 1933 the ISK’s office at Leonard Nelson’s old Göttingen address was searched by Hitler’s brownshirts. Publications were taken from the premises to provide kindling for a later public book burning.¹⁶ A training school for the ISK located in northern Hesse was seized. The facility, known as the Walkemühle, provided political instruction for ISK cadre and housed a school for children, run on Nelsonian principles. In early 1933, Walkemühle teachers, along with their young students, left Germany to continue their tuition in exile, first in Denmark and later in England. The adult courses had already been wound up years previously, when ISK membersin-training were funnelled into practical anti-Nazi work. Children’s political indoctrination continued in a darkly ironic form: the mill that once housed the ISK school became a Hitler Youth camp. 

The ISK’s response was characteristic: it organised a nationwide series of clandestine philosophy seminars to clarify the tasks demanded by the moment.¹⁷ The instructors included Grete Hermann, a pioneering figure in quantum  physics.¹⁸ At the same moment Hermann accepted great personal risk to guide these seminars on the ethics of anti-Nazi resistance, she was drafting a manuscript defending Kantian notions of causality in the face of new theories in quantum mechanics.¹⁹ It is an example of the intellectual calibre of those who were drawn to the ISK and the astonishing sense of purpose that guided its activists.

Other prominent members of the ISK continued their work in exile. This included Nelson’s two leadership successors: Willi Eichler, who directed the ISK’s political activities from a new base in Paris, and Minna Specht, who as chief educational theorist of the ISK guided the children’s school throughout its continued existence beyond Germany. This bifurcated leadership reflected a notable fact of the ISK membership: the numbers of men and women were far more balanced, and the women more likely to occupy leading roles, than within other left-wing organisations of the time.²⁰

The ISK readied themselves for illegality even before 1933 and began organising its resistance network shortly after Hitler took power. This network was led by Fritz Eberhard and Julius Philippson, both associates of Nelson since the First World War, and René Bertholet, a young and charming Swiss graduate of the ISK training school. They were supported in their work, and their movements, by the men and women connected with the ISK’s network of food enterprises, chiefly the ‘Vega’ restaurants. The ITF, the global transport workers’ union led by Edo Fimmen, then headquartered in Amsterdam, provided a vital lifeline to the network in the form of transport routes for smuggling literature and people in and out of Nazi Germany. France and Britain were the centres of ISK coordination in exile. Activists gathered in the Restaurant Végétarien, located on one of Paris’ grand boulevards; the Vega restaurant on London’s Whitcomb Street; and a further restaurant in Amsterdam. 

Within Germany, the ISK network mounted a courageous and costly opposition to the Nazi regime. The chief method was agitational propaganda. Smuggled publications were distributed, street pamphlets were surreptitiously circulated, and graffiti was daubed that assured anti-Nazi Germans that they were not alone: organised resistance to Nazism still existed. Outside Germany, the ISK broadcast a message that there was another Germany, one that held Hitler and his thugs in contempt. Using its live networks within Germany, the ISK in exile also broadcast details of Nazi terror. In Britain, the ISK called for a boycott of German goods and an end to holidaymaking in Nazi Germany in response to Nazi antisemitism.²¹

The ISK underground network remained largely active until 1938 when the Gestapo finally quashed the ISK’s activities and arrested one leader, Julius Philippson, and many activists. Fritz Eberhard, the other active leader, managed to flee, eventually making it to Britain where he contributed to German broadcasts for the BBC. Philippson, a veteran of the First World War from a Magdeburg Jewish family, provided an ideal antagonist for the Nazi court. ‘Led astray by the Jew’ was how the Nazi rag the Völkischer Beobachter characterised the ISK members on trial in 1938.²² Philippson was charged with preparing high treason, convicted, and later deported to Auschwitz, where he was murdered.

In the final analysis, the ISK’s resistance must be categorised as a defeat. Within Germany, they were crushed. While veterans of the underground became valuable recruits for the British and US war efforts, the Allied victory did not hinge upon a small number of committed emigres. The ISK’s appeals for a renewal of Kantian ethics did not defeat the Nazis. The combined military power of the Allied forces did.

Yet in requiring more of its members than would an ordinary Party, Nelson cultivated an elect of individuals free of the attachments and dependencies that obstructed lives of intense political activism. When Nazism arrived in place of the society they desired, those same preparations underpinned a tightly knit community ready for the self-sacrifice that a life of clandestinity and resistance demanded. The movement suited the moment in ways that no longer fit the patterns of politics today. A strange and difficult-to-replicate amalgam of philosophical education, hierarchical politics, animal welfare and community bonding made the ISK, for a while, a remarkably durable resistance organisation.

Perhaps asking how people resisted Nazi authoritarianism provides fewer useful lessons than asking why people took this stance. Within that framing, the history of the ISK offers a great deal. We may reject many of the ISK’s conclusions to the question of how should we live, yet the basic method by which they arrived at such conclusions remains vitally resonant. For the many ISK members who committed themselves to dangerous and noble lives of resistance, how to live was analytically secondary to the question of why should we live. 

Leonard Nelson’s philosophy gave his followers an individually articulated and sincerely felt answer. ISK members modelled their actions in service to a notion of justice wherein all sentient beings – human and animal – had a natural right to be free from exploitation. As Ludwig Linsert, the ISK member whose memories opened this essay, thought to himself in his Gestapo cell: if justice perishes then humanity loses its reason to exist. Pursuing this vision of justice led Linsert and his comrades to philosophical conclusions we may rather avoid and to moral scenarios we must hope never to face; yet the vision remains a potent reminder of how emancipatory politics always demands a clarity of purpose. Or, as Julius Philippson put it in a letter to a comrade written many years before his activism would lead him to Auschwitz: ‘Fort mit jeglicher Unklarheit über das, was wir wollen!’, Away with any ambiguity about what we want!²³

Maurice J. Casey is a historian and writer based in Belfast. He is a Research Fellow at Queen’s University Belfast, where his AHRC-funded project explores the ISK. He received his doctorate in History from the University of Oxford in 2020. In 2024 his first book Hotel Lux: An Intimate History of Communism’s Forgotten Radicals was published by Footnote Press.

Notes

1. I use here Mary Gregor’s translation of Kant’s original, which appears in Immanuel Kant, Metaphysics of Morals, trans. Mary Gregor, ed. Lara Denis, Cambridge University Press, 2017, p332.
2. Ludwig Linsert, ‚Aus Meiner Widerstandsarbeit‘ in Winderstand und Verweigerung in Deutschland 1933 bis 1943, Richard Löwenthal and Patrik von zur Mühlen, J. H. W. Dietz, 1982, p82.
3. See for example: Werner Link, Die Geschichte Des Internationalen Jugend-Bundes (IJB) Und Des Internationalen Sozialistischen Kampf-Bundes (ISK) ; Ein Beitrag Zur Geschichte Der Arbeiterbewegung in Der Weimarer Republik Und Im Dritten Reich, A. Hain, 1964 and Karl Heinz Klär, ‘Zwei Nelson-Bünde: Internationaler Jugend-Bund (IJB) und Internationaler Sozialistischer Kampf-Bund (ISK) im Licht neuer Quellen’, Internationale wissenschaftliche Korrespondenz zur Geschichte der deutschen Arbeiterbewegung, 1982, pp310–59.
4. On the ISK’s UK offshoot, the Socialist Vanguard Group, and its influence on the direction of the Labour Party, see for example: R. M. Douglas, ‘No Friend of Democracy: The Socialist Vanguard Group 1941-50’, Contemporary British History, 16/4, 2002, pp51–86 and Lawrence Black, ‘Social Democracy as a Way of Life: Fellowship and the Socialist Union, 1951–9,. Twentieth Century British History, 10/4, 1999, pp499–539. 
5. Su Lin Lewis, “Women, Hospitality and The Intimate Politics of International Socialism, 1955–1965,” Past & Present, 262/1, 2024, pp242–280. On the philosophical education branch of the ISK in Britain, see: Dieter Krohn, ‘The Society for the Furtherance of the Critical Philosophy (SFCP): A Foundation of German Female Refugees and their British Comrades in 1940’, in Exile and Gender II: Politics, Education and the Arts: 18, eds. Charmian Brinson, Kana Barbora Buresova, and Andrea Hammel, Brill, 2017, pp4–20.
6. For an account of the ISK’s philosophical practice, see: Ferando Leal, ‘Leading a Philosophical Life in Dark Times: The Case of Leonard Nelson and His Followers’, in Philosophy as a Way of Life: Ancients and Moderns, eds. Michael Chase, Stephen R. L. Clark, Michael McGhee, Wiley, 2013, pp184-209.
7. Maurice J. Casey, Hotel Lux: An Intimate History of Communism‘s Forgotten Radicals, Footnote, 2024
8. See my own BBC Radio 4 documentary on Fimmen’s family life: ‘The Alpenpost: A Girl’s Guide to Fighting Hitler and Stalin’, BBC Radio 4, March 8, 2026.
9. Nelles’ work offers a superbly detailed history of trade-union contributions to anti-fascist resistance: Dieter Nelles, Widerstand und internationale Solidarität. Die Internationale Transportarbeiter-Föderation (ITF) im Widerstand Gegen Nationalsozialismus, Klartext Verlags, 2001.
10. Klär, ‘Zwei Nelson Bunde‘, p317.
11. Tom, Kathy and Peter Pfister, Eva and Otto: Resistance, Refugees, and Love in the Time of Hitler, Purdue University Press, 2019, p15.
12. Marcus Willaschek, Kant: A Revolution in Thinking, Cambridge, Harvard University Press, 2025, p97.
13. Leonard Nelson, System of Ethics, trans. Norbert Guterman, Yale University Press, 1956, p143.
14. “Nelson Memorial Meeting,” ca. July 1942, Pfister Family Papers, Tom Pfister Personal Archive. Thank you to Tom Pfister for sharing this transcript.
15. For Nelsonian anti-democracy in English, see: Leonard Nelson, Politics and Education, trans. W. Landsell, Routledge, 2018 (First published 1928), pp23-66.
16. Rainer Driever, ‚Polizeiliche Beschlagnahmung „staatsfeindlichen Vermögens“ in Göttingen ab 1933‘, Beschlagnahmungen - Rainer Driever selbständiger Historiker, Accessed 17 June 2026.
17. Antje Dertinger, Die drei Exile des Erich Lewinski; The Three Exiles of Erich Lewinski, trans. Tom Lewinski, Privately produced English translation, Original published 1995, p79.
18. Dertinger, Die drei Exile, p79.
19. Elise Crull, ‘Grete Hermann’s Interpretation of Quantum Mechanics’, in The Oxford Handbook of the History of Quantum Interpretations, ed. Olival Freire, Oxford University Press, 2022, pp567-586.
20. Historian Layla Kiefel recently completed a French-language thesis on the history of women in the ISK, see: bKiefel, Les femmes de l’Internationaler Sozialistischer Kampfbund de la République de Weimar à la République fédérale : engagement, résistance, emancipation, PhD diss, Université Bordeaux Montaigne and Universität Konstanz, 2024.
21. Calls for the boycott appear in adverts in late 1938 issues of Socialist Vanguard, the publication of the ISK’s British branch the Militant Socialist International.
22. Völkischer Beobachter, 7 December 1938, Bundesarchiv, R58/373.
23. Klär, ‘Zwei Nelson-Bünde‘, p313.