In the previous chapter we saw Aquinas unearth in his Commentary and appropriate in his ST Aristotle's first political-philosophic foundation in Politics I: the relative yet real naturalness of civic life for human beings, and the close link between this naturalness and that proper to the virtues, about which more will be said in the last part of this chapter. In this chapter I explore another political-philosophic foundation common to both Aristotle and Aquinas, and from that vantage point begin to question the absolute affinity between Aquinas's and Aristotle's foundations for political theory. My analysis focuses first on Aquinas's more ambivalent response to Aristotle's second civic foundation in the distinct natures and requisites of political regimes and their corresponding versions of political virtue. I argue that as a consequence of finding faults in Aristotle's second foundation, Aquinas defers or declines to comment on Aristotle's science of the absolutely best regime – the Philosopher's third political-philosophic foundation in Politics VII and VIII. Instead, Aquinas sets out to reinforce an Aristotelian grounding for politics with a new ethical foundation of his own: his theory of natural law and the human inclination toward moral virtue.

The argument of this chapter commences with what I have termed Aristotle's second foundation: the centrality of regime particularity, citizenship, and civic virtue to politics and political science, as elaborated in Book III of the Politics and the corresponding sections of Aquinas's Commentary.