  The Principles appeared in Latin in 1644, with a French translation following in 1647. Descartes added to the French translation an “Author's  Letter” to serve as a preface. In the letter he explained important elements of his attitude toward philosophy, including the view that in matters philosophical one must reason through the arguments and evaluate them for one's self (9B:3). He also presented an image of the relations among the various parts of philosophy, in the form of a tree: