It is a commonly held view that Kant's system of metaphysics, as expounded in his Critique of Pure Reason and subsequent work, was definitively refuted by the late 19th and early 20th century developments in mathematics and the natural sciences. Thus his characterisation of geometry as a body of synthetic a priori truth is supposed to have been shown false by the discovery of non-Euclidean geometries, and by their application to the general theory of relativity.

The development of quantum theory, the focus of this talk, on the other hand, is supposed to have invalidated Kant's belief in the synthetic a priori status of the principle of causality. In my talk I argue that the truth is more subtle. There are, in fact, important affinities between Kant's philosophical views and the views of one of the fathers of quantum theory, and the principal proponent of its dominant 'Copenhagen interpretation', Niels Bohr.

In particular, I argue that one can justify, on Kantian grounds, Bohr's central dictum that quantum concepts do not pick out objects in the ordinary sense of the word. One can ground Bohr's claim, that is, in the fact that in Kant's system, phenomenal experience which is not fully determinable in accordance with his 'principles of the pure understanding', cannot also be called objective experience.

Ultimately, I argue, Bohr's Copenhagen interpretation of quantum theory---including its restriction on the legitimate use of the principle of causality---is perfectly compatible with, and indeed follows naturally from a broadly Kantian epistemological framework (although the result would likely not have been an altogether satisfactory one for Kant).