Descartes corresponded with Princess Elizabeth of Bohemia, who was very interested in applying his doctrines for clear thought. As a result of this exchange, he wrote The Passions of the Soul (1669), which was an account of how the mind worked and was connected to the body.

In the same year, Descartes agreed to move to Stockholm to tutor Queen Christina. Like Princess Elizabeth, she was drawn to Descartes’ ideas, and wished to be well-informed and educated, in general. A small pension from the King of France had been delayed for many years, and Descartes needed the funds, as well as the honor of royal patronage. He called Sweden “the land of the bears” and was much inconvenienced by demands of the athletic young queen that he begin his lessons for her at 5:00 A.M. Descartes had always been a late riser, preferring to begin his day by reflecting in bed until noon. When he was a student at La Flèche, he had been given special permission not to rise early. Descartes’ biographers believe that the change in his routine weakened him. He caught pneumonia and soon died.