This article discusses the influence of Koyré’s epistemology on Lacan’s conception of the real and more broadly on his critical examination of the relation between science and psychoanalysis. The discussion necessitates a systematic return to Koyré, whose visibility in contemporary philosophical and psychoanalytical debates is rather marginal despite his major contribution to the development of epistemology, philosophy and structural psychoanalysis in 20th century France and beyond. The article embeds Lacan’s teaching in a broader intellectual movement of French philosophy of science, which already recognised the necessity of a materialist epistemology. Following this current, Lacan openly associated his take on structuralism with dialectical materialism. Or, this positioning of psychoanalysis can hardly be understood in its overall complexity without re-examining Koyré’s philosophical and epistemological polemics and the influence of his historical examination of the foundations of modern science on mid-20th century structuralism. The latter, one could argue, repeats the modern astronomical revolution in the field of human objects (language, thought, society). Lacan’s structural psychoanalysis was undoubtedly the most radicalised version of this repetition – but precisely this would not have been possible without Koyré’s historical epistemology.