The changing places thought experiment was conceive of by Max Velmans, Professor of Psychology at Goldsmiths College, University of London, and was discussed in his 2000 work, Understanding Consciousness. The experiment was designed to demonstrate the difficulties in distinguishing phenomenologically between a first-person experience of an event (a subjective experience of an object) and a third-person experience of the same (that is, the observation of such an experience in a subject).