 In the Arabic tradition, Aristotelian logic was at first studied by close reading of Aristotle’s own texts, but Avicenna then replaced Aristotle as the authority, and then often later textbooks replaced his work  (§1.1).  Almost the reverse process took place in the Latin world. From consisting mainly of encyclopaedic accounts, the logical syllabus moved to being constituted of a couple of Aristotle’s works, supplemented by Porphyry and Boethius (the logica vetus) by the eleventh century, and once the rest of the Organon (the logica nova) became available, by the early thirteenth century, Aristotle’s logic (augmented just by Porphry’s Introduction and a twelfth-century text supplementing the Categories) was studied in detail in the universities, continuing to the sixteenth century, and even later in Spain. This tradition of commentary, although never abandoning Aristotle’s text, often resulted in sorting out the difficulties in his presentation and reworking his logic (as, for example, in the commentary on the Prior Analytics by  Robert Kilwardby  from the 1240s: see Thom  2019).[37]