Of the top five global thinkers, four were philosophers: Slavoj Žižek, Daniel Dennett, Jürgen Habermas and Peter Singer himself. (The non-philosopher, hilariously, was Al Gore.) The rankings, inevitably, are based on social media and other internet measures, so are open to challenge, but they tell us something about who is being watched, talked about and read. Singer concludes from the remarkable prominence of philosophers in the public sphere that the billion or so people who don’t have to worry about food and other basics are hungry for answers to the great questions of life, a hunger that only philosophy can satisfy. “I know from my own experience,” Singer writes, “that taking a course in philosophy can lead students to turn vegan, pursue careers that enable them to give half their income to effective charities, and even donate a kidney to a stranger. How many other disciplines can say that?”

Singer is right — but his argument cuts both ways. Philosophy certainly can do such things, but it can also turn students into stormtroopers. The most influential German philosopher of the 20th century, Martin Heidegger, is a case in point. As the most original pupil of Edmund Husserl, the founder of phenomenology, Heidegger became a celebrity with his first book, Being and Time; but what he did with his fame, including his betrayal of his teacher and other Jewish colleagues, will live in infamy. When Hitler took power, Heidegger became a Nazi and as Rector of Freiburg University tried to align the German universities with National Socialism, which he saw as a world-historical resistance movement against the depredations of modernity. At the end of the war, Heidegger lost his chair, but as his Nazi past receded he came to exercise a unique sway over Continental intellectual life. Yet though his prestige grew steadily, largely thanks to Jewish former pupils such as Hannah Arendt and admirers such as the poet Paul Celan, he never repudiated that part of his past and died unrepentant in 1976.

For better or worse, Heidegger’s ideas live on, not only in his writings but also through those of his students. One of these, Ernst Nolte, has just died in August aged 93. Nolte is best known as a historian, but his doctorate was in philosophy and Heidegger was by far the most important influence on his life and work. As a student, Nolte was responsible for helping Heidegger and his wife to escape arrest by the French at the end of the war; he remained a family friend. In the 1960s Nolte gained an international reputation as a historian of fascism, but by the time I arrived at the Free University in Berlin in 1979-80, he was already notorious for his reactionary, though not yet neo-Nazi, sympathies.

I attended several of his lectures on a collection of texts about fascist ideology, which he was among the first scholars to take seriously. He made quite an entrance, preceded by a procession of favoured students carrying his books and notes. His delivery was dry and old-fashioned but the content was provocative. Nolte argued that fascism and communism were both opposition movements to Western liberal democracy, but that Lenin and Stalin were both more original and more radical in their methods than Mussolini and Hitler. I found Nolte tendentious and soon stopped attending his lectures; I later heard that protesters had brought the course to a premature end. Nolte seemed to relish such notoriety, though not when the Autonomen blew up his car in 1988. Rather than blame these masked anarchist thugs, he denounced the “intellectual initiator” of the attack, the left-liberal historian Hans-Ulrich Wehler. That this was an unfounded accusation did not stop him making (and some believing) it.