In 1643, Princess Elisabeth of the Palatinate asked the philosopher René Descartes for some explanations about his theories on the distinction about the body and the mind – the same mind he had made the starting point for the confirmation of all knowledge in his Cogito ergo sum argument (“I think, therefore I am”). Elisabeth, who had come to La Hague, Netherlands, as a refugee with her family, had met Descartes during one of his visits. They discussed mathematics and philosophy, and kept corresponding by letters. In 1643, she was 25 and he 47.