The correspondence between Elisabeth of Bohemia (princess of the Palatinate) and Rene Descartes (famous philosopher) is worth reading, at least in parts, for any student of modern philosophy. It presents an incisive critique of Descartes' unity of mind and body, a response giving a unique insight into Descartes' metaphysics, a further critique, and then breaks off! (We are left to wonder how or when the conversation continued.) The rest is very interesting to read, but deals with less sharp areas of philosophy.