A classic study of the history of psychology by Brett, written in 1912-20 , well before the seminal work by Kuhn, states that ‘it is more in keeping with the history of thought to describe science as the myths about the world which have not yet been proved to be wrong’.188'37 This seems at first sight to accord with the wellknown arguments by Karl Popper that science can only be known as true science by the possibility that its main assumptions can be disproved: that it is an open system of knowledge rather than a closed one. He defines a closed system of thinking - including Freud, Marx and Adler, as well as Plato - as a system that is so comprehensive that no happening in the world can disprove it. A Marxist would have her or his own interpretation for anything that occurred, just as the Freudian would have his or her quite different one: whatever happened, each would leave the scene with his or her conceptual world intact.