"This project aims at a deeper understanding of Niels Bohr’s philosophical thought on quantum mechanics. Bohr was one of the creators of what is known as the old quantum theory, developed in the years 1913–1925, and one of the most influential interpreters of the new quantum theory, which was developed in 1925–1927 and is the version accepted by physicists today.Though influential, Bohr’s thoughts on quantum mechanics are notoriously difficult to understand. The current project will shed light on Bohr’s thought by viewing it within a framework informed by the philosophy of symbolic forms of the neo-Kantian philosopher Ernst Cassirer, and the revision of Kantianism due to Michael Friedman, which is also inspired by Cassirer, although alternative views also shall be considered. The chief difference between this revised Kantianism and the philosophy of Kant is that, whereas for Kant the conditions for the possibility of experience, through which we make sense of talk of objects of experience are fixed and immutable, in the revised version they develop along with the development of science.The core of the project will involve an examination of the status of the correspondence principle, a crucial ingredient in the transformation of the old quantum theory to the new quantum theory. The correspondence principle requires agreement, in some respect, between classical mechanics and quantum mechanics in the limit of large quantum numbers. The result of the project will not only be a deeper understanding of Bohr’s thought and the development of quantum mechanics; there will be broader implications for understanding the development of science."