 The idea that discrepancies in Aristotle’s texts are due to the development of his philosophy was as alien to Alexander as it was to all other thinkers in antiquity. Instead, he treats Aristotle’s philosophy as a unitary whole and tries to systematize it by forging together different trains of thought, and smoothing over inconsistencies. Thereby he contributed to the emergence of what was to become the canonical ‘Aristotelianism’ that was attacked in early modern times as a severe obstacle to new ideas and scientific development. Though Alexander indicates that he was aware of changes at particular points (he regarded the Categories as Aristotle’s earliest work and notes that it does not yet observe the systematic distinction between genus and species), he does not consider the possibility that there were different phases with substantial changes in the Master’s work. If such conservatism surprises us in view of the fact that Alexander’s own work shows traces of revisions and improvement, we must keep in mind that in the eyes of ‘The Commentator’ Aristotle was an authority quite outside the common order. The doctrine of the Master was not the product of an ordinary human mind, subject to trial and error, but a magisterial achievement in a class of its own.