 Now, Newton’s theory of gravitation, Einstein’s relativity theory, quantum mechanics, Marxism, Freudianism [the last two stock examples of bad science or pseudo-science for Popperians], are all research programmes, each with a characteristic hard core stubbornly defended, each with its more flexible protective belt and each with its elaborate problem-solving machinery. Each of them, at any stage of its development, has unsolved problems and undigested anomalies. All theories, in this sense, are born refuted and die refuted. But are they [all] equally good? (S&amp;P: 4–5.)