In the course of 1934, Grete Henry-Hermann, a young German pupil of Leonard Nelson trained in philosophy as well as in mathematics and physics, visited Heisenberg in Leipzig, with the intention to call Kant before the tribunal of history, hoping to be able to conciliate transcendental philosophy with the new quantum physics. Do Kant's propositions still hold good for a physics which seemed to break so radically and scandalously with the principles of the physics retrospectively called ‘classical’? Grete Henry-Hermann's attempt to confront quantum physics with Kantian philosophy is, chronologically, one of the first: she was truly a pioneer in engaging in a philosophical interpretation of quantum physics. The paper presents and criticizes the positions of Grete Henry-Hermann, and especially: (1) her original attempt to save the Kantian category of causality, by on the one hand retaining the universal validity of the pure concept of causality, while on the other hand accepting, with Bohr and Heisenberg, the definitive character of statistical predictions. Her attempt consists in showing that once a result has been actually obtained, it is possible, by working backwards, to reconstitute, retrospectively and completely, the causal chain which has necessarily produced such a result; (2) her refutation of the so-called von Neumann's proof. Grete Henry-Hermann's essay of 1935 contains the first critique of von Neumann's argument which aimed to demonstrate the impossibility of completing quantum physics by means of hidden parameters, and which has been regarded as firmly established until 1964, that is, until the year Bell published his famous refutation. Yet, reading Grete Henry-Hermann's essay, one discovers that in 1935, thirty years before Bell, Grete Henry-Hermann had produced a refutation of von Neumann, based on arguments very similar to those of Bell in 1964. Had Grete Henry-Hermann's refutation not remained a dead letter, the history of the interpretations of quantum physics would certainly have been very different.