Averroes's Commentary on Plato's“Republic” goes far beyond merelycommenting on the original. With the benefit of1,500 years of hindsight, it reckons with importantworks of philosophy that would have been completelyunknown to Plato. Averroes mentions three authors ofsuch works by name: Galen, whom he mostly rebukes,Aristotle, and Alfarabi. It would be hasty to assertthat by including such extraneous material, Averroesdeparts from Plato, but, at the very least, heupdates him on account of historicaldevelopments.

The importance of Averroes's post-Platonic additions isevident from the very structure of the work. Thepart of it that can plausibly claim to be acommentary on Plato does not begin until 27.24,almost seven pages into Rosenthal's Hebrew text.Averroes begins to address the subject of war,corresponding to Republic 374b, having skipped all ofbook 1 and the majority of book 2, with only twobrief references to them in the opening section (CR22.27–30, 23.31–33, cf. 47.29–30and 105.25–27).Averroes does not justify his omission until thevery end of the work, when he states that theopening part of the Republic does not contain any of thedemonstrative arguments of which his commentary iscomprised (CR 105.25–27, cf. 21.4). He is moreimmediately forthright about the reasons for what heincludes in its place. In keeping with thedemonstrative focus of the work, Averroes replacesPlatonic dialectic with a substantial discussion ofscience. Having divided practical science into twoparts, one about general habits and actions andanother about their implementation, Averroesexplains: “Before we begin a point-by-pointexplanation of what is in these arguments [ofPlato], we ought to mention the things pertinent tothis [second] part [of practical science] andexplained in the first part, that serve asfoundation for what we wish to say here at thebeginning” (CR 22.6–8). Averroes's introductionconcerns above all the first part of politicalscience, while the Republic proper contains only thesecond. Averroes attributes to Plato only a smallpart of the ensuing discussion, concerning justice,the division of labor, and the arrangement of thesoul (CR 22.22–24.6, esp. 22.27, 23.31). The otherpassages are inspired by Aristotle and especiallyAlfarabi. Averroes appears to substitute scientificarguments from Aristotle and Alfarabi—mainly aboutscience, philosophy, courage, and war—for Plato'sdialectical introduction about justice and thefounding of the just city.