By breaking decisively with the predominantly apologetic and hagiographic literature on science during National Socialism and employing compelling terms such as “irresponsible purity” and “collaborative relations,” Herbert Mehrtens profoundly influenced both his contemporaries and the subsequent generation of historians working in this field.

Herbert Mehrtens‘ work and the implications of the historical ideas he advanced went beyond the history of any single discipline. The article therefore addresses three broad issues: (1) Mehrtens‘ reconceptualization of mathematical modernism, in his field-changing book Moderne—Sprache—Mathematik (1990) and other works, as an epistemic and cultural phenomenon in a way that could potentially reach across and also beyond the sciences and also link scientific and cultural modernisms; (2) the extension of his work to the history of modernity itself via the concept of “technocratic modernism”; (3) his seminal contributions to the historiography of the sciences and technology during the National Socialist period, focusing on his critique of claims that mathematics, the natural sciences and technology were morally or politically “neutral” during or after the Nazi era, and on his counter-claim that mathematicians and other scientists had in fact mobilized themselves and their knowledge in support of Nazism’s central political projects. Taken as a guide for understanding science-politics relations in general, Mehrtens‘ work was and remains a counterweight to the political abstinence adopted by many who have followed the “cultural turn” in history of science and technology. In the broadest sense, the article is a plea for the culturally relevant and politically engaged historiography of the sciences and humanities that Mehrtens himself pursued.

In the decade between 1983 and 1993, Herbert Mehrtens in West Berlin and I in East Berlin communicated closely about our parallel work on mathematics under the National Socialist (NS) regime. For a short period (1988–89), we worked on a joint book on this topic. We agreed that the book should be based primarily on empirical historical material, using a theoretical approach largely guided by Mehrtens’ work on social systems in mathematics (Mehrtens1981, 1987a). However, parallel work for his habilitation thesis on modernity in mathematics increasingly captivated Mehrtens’ interests. This, together with ongoing resistance among older mathematicians and the insecurities of our individual careers during times of considerable political change, particularly in East Germany, led to the failure of our joint project.

This paper aims at reconstructing—mostly by drawing on correspondence—parts of the dialogue between Mehrtens and me at the time. Our dialogue was influenced by our different upbringing and socialization in the two parts of Germany, and by different, though complementary, views about the combination of empirical and theoretical approaches to the historiography of mathematics.

In the epilogue, I describe how my later work in the decades from the 1990s on the history of mathematics profited much from Mehrtens’ early theoretical and empirical work but was less influenced by his book on modernity. That later work of mine was, however, mostly done at a time when Mehrtens had largely left the field and considered himself increasingly as a “cultural scientist” (Kulturwissenschaftler).

What kind of mathematical research activities took place in prisoner of war camps in Germany during the Second World War? And can one inspect such activities in order to re-examine, on the one hand, Herbert Mehrtens’ analysis of the modernism/counter-modernism divide of early twentieth-century mathematics, and on the other, his research on the instrumentalization of mathematics during the war? Closely examining the work carried out in the field of algebraic geometry by the French mathematician Bernard d’Orgeval, who was held in three of such camps between 1940 and 1945, the paper aims not only to unfold this unique episode in the history of mathematics, presenting it as an ephemeral configuration, but also to show the limitations of Mehrtens’ approach and the narrative of modern and counter-modern mathematics.

Epistemological issues associated with Cantorian set theory were at the center of the foundational debates from 1900 onward. Hermann Weyl, as a central actor, saw this as a smoldering crisis that burst into flames after World War I. The historian Herbert Mehrtens argued that this “foundations crisis” was part of a larger conflict that pitted moderns, led by David Hilbert, against various counter-moderns, who opposed the promotion of set theory and trends toward abstract theories. Among counter-moderns, L.E.J. Brouwer went a step further by proposing new foundational principles based on his philosophy of intuitionism. Meanwhile, Felix Hausdorff emerged as a leading proponent of the new modern style. In this essay, I offer a reassessment of the foundations crisis that stresses the marginal importance of the various intellectual issues involved. Instead, I offer an interpretation that focuses on tensions within the German mathematical community that led to a dramatic power struggle for control of the journal Mathematische Annalen.

It would have been easy for a less imaginative historian of mathematics than Herbert Mehrtens to have portrayed the work of Hilbert, Hausdorff, and other modernists as pioneers, and those who did not subscribe to their program as people who failed, were not good enough to make the turn, and were eventually and convincingly left behind. That he did not do so is not only because this would have been a shallow, selective view of the facts: it is incompatible with his Foucauldian approach to the relations between knowledge and power. Instead, he defined what I see as the most intriguing category of actor in his Moderne—Sprache—Mathematik (1990), the Gegenmoderner, or counter-moderns. The three men who characterize this position are Felix Klein, Henri Poincaré, and Luitzen Brouwer, and each merits a section in the book.

Of the three, Poincaré is the hardest to contain within that category. The range of his work, the nature of his influence, and the shifting standards by which mathematical significance has been evaluated by mathematicians, historians of mathematics, and society at large, all contribute to the problem. After thirty years, the methodological presumptions and aspirations of historians of mathematics have also changed, and I shall suggest that one way to appreciate the richness of Mehrtens’ book, to gain insight into what is meant by mathematical modernism, and to acknowledge a generation of work by other historians since 1990, is to re-examine aspects of Poincaré’s life and work and scholarship about him. Prodded by remarks by Leo Corry, Moritz Epple, and David Rowe, I shall suggest that the simple but useful dichotomy modern/counter-modern must be seen as a way into a more complicated situation, one in which different aspects of mathematics, specifically applied mathematics and the relationship of mathematics to contemporary physics, require fresh accounts of the role of modern mathematics in society.

This essay takes inspiration from Herbert Mehrtens’ 1995 claim that the “history of mathematics is an integral part of intellectual history.” It asks why, despite the tremendous transformation the historiography of mathematics has undergone since the field began to professionalize in the 1970s, historians of mathematics repeatedly complain that their field has been marginalized. The answer, I suggest, is not due to the fact that mathematics is less amenable to the types of social, cultural, or material analysis that came to dominate the history of science in recent decades. Rather, at issue is that most historians have adopted mathematicians’ own definition of mathematics. The history of mathematics professionalized at a particular moment, one in which mathematicians were concerned about the limits and boundaries of their field. As such, they were invested in drawing boundaries around the “proper” confines of the field. Historians of mathematics have followed suit, and similarly restricted what did and did not belong in the history of mathematics. Following Mehrtens, however, and insisting that the history of mathematics is an integral part of broader intellectual history, a more capacious conception of the field is possible.