Aelius Donatus
Much of medieval thought in philosophy and theology can be found in scholastic textual commentary because scholasticism was such a popular method of teaching. Aelius Donatus' "Ars grammatica" was the standard textbook for grammar; also studied were the works of Priscian and "Graecismus" by Eberhard of Béthune. Cicero's works were used for the study of rhetoric. Studied books on logic included Porphyry's introduction to Aristotelian logic, Gilbert de la Porrée's "De sex principiis" and "Summulae Logicales" by Petrus Hispanus (later Pope John XXI). The standard work of astronomy was "Tractatus de sphaera".