In the 1960s and 1970s the protagonists of what has later become known as the “new philosophy of science” gave rise to a wide and rich debate that involved several philosophers from different countries. Since the present work aims at offering a critique of one of the characteristic theses of the post-Popperian philosophy of science, and particularly Kuhn’s interpretation of it, I need first to analyse in some detail the positions of the other participants in the debate and how they influenced Kuhn’s own position. I will do that by paying particular attention to a key moment: the International Colloquium in the Philosophy of Science held in London in 1965, which saw the meeting (and the clash) of some of the most important philosophers of science of the twentieth century.