Johannes Cotto (John Cotton, Johannes Afflighemensis; ) was a music theorist, possibly of English origin, most likely working in southern Germany or Switzerland. He wrote one of the most influential treatises on music of the Middle Ages, De musica, first printed by Gerbert in 1784. The treatise included unusually precise directions for composing chant and organum. Life Next to nothing is known about his life; indeed his identity has been a matter of controversy among scholars. Formerly it was thought he was from Lorraine or Flanders, based on a dedication he made in his treatise, but other more recent evidence suggests that he may have been a John Cotton from England who worked under an abbot named Fulgentius at or near St. Gallen (in modern Switzerland). Some of the more compelling evidence includes his knowledge of chant peculiarities of that region, notational idiosyncrasies found only in southern Germany, and his use of the old Greek modal names such as Phrygian and Mixolydian, something which was mainly done in Germany. Works and influence His De musica was one of the most widely copied and distributed music treatises of the medieval period, with some copies appearing even after 1400. Most likely it was written around 1100, and its comments, examples, and suggestions correspond closely with the music of the contemporary St. Martial school and Codex Calixtinus, as well as the material in the treatise Ad organum faciendum (also known as the "Milan Treatise") from about the same time. De musica consists of twenty-seven chapters, and covers a wide range of musical topics. Unlike many medieval treatises, it largely avoids metaphysical speculations, instead functioning as a practical guide for a working musician. Much of the source material is from Guido of Arezzo, Boethius, Odo of Cluny, Isidore of Seville, and Hermannus Contractus. After chapters on 'litterae' (letter notation), monochord, nine 'consonant' intervals (unison, semitone, whole tone, ditone, semiditone, diatessaron, diapente, semitone-plus-diapente, whole-tone-plus-diapente), the Perfect System (systema teleion) of Greeks, musical modes (including a chapter on their ethos), and the composition of chant, the treatise includes one chapter most of interest to contemporary scholars: a detailed description of how to compose organum. Most of his examples are note-against-note, and demonstrate how to end on a fifth or an octave by good voice-leading; he emphasizes the importance of contrary motion, a practice which differed from the parallel organum of the preceding centuries (though it probably