When I started my studies in the philosophy of science in the early fifties, it was quite clear to me that logical positivism was the leading school in the philosophy of the natural sciences. This conception was strongly promoted by the Vienna Circle between 1923 and 1938, as well as later when the events leading to World War II saw the Circle members leaving Vienna and establishing themselves all over the world, particularly in the United States. In the United States, Carnap would soon become a leading figure, whereas in England, Popper eventually would become the main proponent.