 There is an interpretational tradition which holds that Descartes only took the first, ‘ordinary’ sense of motion seriously, and introduced the second notion to avoid conflict with the Catholic Church. Such conflict was a real concern, since the censure of Galileo’s Copernicanism took place only 11 years before publication of the Principles, and had in fact dissuaded Descartes from publishing an earlier work, The World. Indeed, in the Principles (III.28) he is at pains to explain how ‘properly speaking’ the Earth does not move, because it is swept around the Sun in a giant vortex of matter – the Earth does not move relative to its surroundings in the vortex.