Professor Karl Popper has had a great deal to endure: “expositions” of his ideas which were mere travesties, “refutations” which he had already answered, by anticipation, or which entirely missed the point at issue. One can easily understand why, when he came to publish an English translation of his Logik der Forschung, he decided to keep to the original text; it should at last be clear exactly what he had—and had not—said in 1934. Yet his thinking had by no means stood still since that time; quite naturally, too, he wished to emphasize as much.