The construction of Pythagorean musical theory rests philosophically on the foundation provided by Sectio Canonis. Indeed, the treatise may have performed this role historically too. Andrew Barker has recently contributed to this journal a discussion of the methods and aims of the Sectio—JHS ci (1981) 1—16. In so doing he has pinpointed lapses in the theoretical reckoning of the treatise, especially in the case of proposition 11 (P11). I should like to reply to Barker's article. My remarks concern the authorship and date of the treatise, the introduction, a few propositions, and ultimately the historical and philosophical settings for the Sectio.