In Copenhagen in 1927 Heisenberg developed his uncertainty principle. In a paper presented at the Volta Conference at Como in September 1927, Bohr demonstrated that the uncertainty principle could be derived from classical arguments, without quantum terminology or matrices. Einstein preferred the determinism of classical physics over the probabilistic new quantum physics to which he himself had contributed. Philosophical issues that arose from the novel aspects of quantum mechanics became widely celebrated subjects of discussion. Einstein and Bohr had good-natured arguments over such issues throughout their lives.