This chapter begins by presenting al-Bataliawsi's text in translation without commentary. It summarizes the rhythmic theory of Ishaq al-Mawsili as a first step towards clarifying al-Bataliawsi's terminology. In 1994 Eckhard Neubauer made a very important discovery regarding the Arabic rhythmic modes practised in Spain in the eleventh- and twelfth-centuries. Given its proven importance in Andalusian musical discourse and practice well into the sixth century AH/ twelfth century AD, it may have a more than analogical application to Western medieval music. Ishaq's original definitions are quite vague in their formulation. He did not use rhythmic notation to clarify his meaning, in contrast to the practice of later theorists who employed letter, prosodie, and geometric notations. Ishaq assigned names to the rhythmic modes-the nameless excluded-when he reorganized and classified the rhythmic and melodic modal system in the course of attempting to write a theory of medieval Arabic music.