Quine was one of the most significant philosophers of the later 20th C. Whitehead supervised his thesis, gave him his first taste of the incomparability of ‘live’ rather than ‘book’ philosophy, and introduced him to his early hero Russell. Further watershed meetings were with Carnap (Quine became his combative disciple and great friend), and Tarski (another great friend). Quine also met Leśniewski and Łukasiewicz in Warsaw, and Gödel and Schlick in Vienna (Wittgenstein never replied). He corresponded with Piaget, Church, Chomsky and Schrödinger, and described his friend Skinner and himself as Harvard’s Tweedledum and Tweedledee.
Bolzano’s pioneering ideas in mathematical logic were only properly appreciated after his death. He did mathematical research under Gerstner, but Austrian state censorship (Bolzano was banished from Prague and from academia for two decades) helped deprive him of contact with his intellectual peers; Abel, Lobachevsky and Gauss all knew of him, without having any direct contact. He was keen to meet Cauchy (their independently-conceived work had much in common), and seemingly did so, when Cauchy arrived for an unrewarding post in Prague. Dobrovský, a key player in Czech national culture, was a keen supporter.
Brunschvicg taught him; Delsarte and Aron were fellow-students. Cavaillès’ ideas had a deep influence on his friend Bachelard. He worked closely with Noether, published Sartre’s first essay, and knew the historian and Resistance chief Bloch personally. Cavaillès’ and his great friend Canguilhem’s professional paths were deeply intertwined. He encouraged Canguilhem into the Resistance; Canguilhem ensured after he was killed by the Gestapo that his work got published, writing a biography and calling him “a philosopher mathematician loaded with explosives, lucid and reckless… if that’s not a hero, what is?”