Casimir Lewy (Polish: Kazimierz Lewy; Warsaw, 26 February 1919 – Cambridge, 8 February 1991) was a Jewish Polish-born British philosopher. He worked in philosophical logic but published scantily. According to Ian Hacking, He had early acquired the conviction that one should publish only when one got something absolutely right, so he left very little in print. He was an influential teacher; several of his students went on to be prominent philosophers, including Roger Scruton, Ian Hacking, Simon Blackburn and Crispin Wright.
His father, Ludwig Lewy, was a doctor and died when he was a boy, so he grew up with his mother's family. After nine years at the Mikolaj Rej school in Warsaw, he travelled to the UK in 1936. He was admitted to the University of Cambridge that year, and graduated in 1939 aged twenty. A doctoral pupil of G. E. Moore to 1943, he attended lectures by Ludwig Wittgenstein from the late 1930s until 1945. During this period, the international situation, as well as the political situation in Poland was rapidly deteriorating. Lewy spent most of the Long Vacation of 1938 in Poland, returning to Cambridge just before the Munich crisis. But it was not until the defeat of Poland in 1939 that he realized he would not be able to return to his native country. Most of his family perished in the Holocaust.
Remaining in the UK, he taught at the University of Liverpool, and then from 1952 at Cambridge as a University Lecturer. He became Doctor of Philosophy in 1943, with an essay entitled Some Philosophical Considerations about the Survival of Death. He also helped Moore as an assistant editor of the journal Mind while Moore was lecturing in the United States, and he participated in meetings of the Moral Sciences Club. He taught at the Faculty of Moral Science in Cambridge in the years 1943–45. He was a Fellow of Trinity College, Cambridge from 1958. He became a Fellow of the British Academy in 1980. In a 2009 interview with Alan Macfarlane, Cambridge philosopher Simon Blackburn said of Lewy "At Cambridge the great influence on all of us in Trinity was Casimir Lewy; he was a Polish Jew who had left Germany just in time before the Second World War. He lost either all or nearly all of his family; he was a charismatic teacher with an enormous influence on a whole generation of philosophy students in Trinity - Ian Hacking, Edward Craig and myself, Crispin Wright - many of us became academics."
- British Academy Biographical Memoir: Ian Hacking, Proceedings of the British Academy 138, pp. 171–177