  In 1643, at the age of forty-seven, Descartes moved to Egmond du Hoef. With the Voetius controversy seemingly behind him (though, as mentioned above, it would again raise its head and climax five years down the road), Descartes and Princess Elisabeth of Bohemia began to correspond. In this exchange, Princess Elisabeth probed Descartes on the implications of his commitment to mind-body dualism. During this time, he completed a final draft of a new textbook, which he had begun three years earlier, the Principia Philosophiae (Principles of Philosophy), and in 1644 it was published. He dedicated it to Princess Elisabeth.