 While it is difficult to determine when Descartes composed his principal methodological treatise, Rules for the Direction of the Mind (Regulae ad directionem ingenii), it is widely believed that he composed the Rules in the 1620s (see Weber 1964: 194–207; Gaukroger 1995: 104–187; Schuster 2013: 307–349). More recent evidence suggests that Descartes may have continued working on the Rules after 1628 (see Descartes ES). Rules contains the most detailed description of Descartes’ method anywhere in his corpus. However, he never completed it, and he never explicitly refers to it anywhere in his published writings or correspondence. 