A letter written by French philosopher Rene Descartes will be returned by Haverford College, Philadelphia, to the Institut de France.
The college has no idea how the letter came to be in its collection, but it appears to be one of thousands of documents stolen and sold by curator Gugliemo Libri in the mid-1800s. It was rediscovered in the course of a document digitization project.
Descartes, a foundational thinker of modern times, famously claimed "I think, therefore I am." In the letter, he seeks guidance from a friend who is a priest about what he can say in his work Meditations on First Philosophy without risking excommunication.