For Aristotle, as seen in chapter 1, the rational content of the law derives from the practical reason of the lawgiver. In the central case, the legislator’s enactments will be oriented by the ends of virtue and human flourishing. Aristotle’s attribution of a decisive role to the practical reason of the lawgiver seems, however, to be in tension with better-known aspects of his political thought. In particular, it is far from self-evident that a robust account of legislative agency is in harmony with political naturalism. The famous assertion in Politics I.2 that there is a natural impulse to form political communities is immediately contraposed with the claim that the person responsible for their foundation is the cause (aitios) of the greatest of goods (Pol. 1253a33). Yet if the polis truly exists by nature and humans are by nature political animals (1253a1-2), then the obvious question arises as to why active intervention by the legislator is necessary at all for a polis. Conversely, if the polis is an artefact of the architectonic legislator’s practical reason, then the distinction between products of the intellect and natural entities seems to preclude the status of the polis as natural. In light of this apparent tension within Aristotle’s account of the origins of political communities, the current chapter seeks to demonstrate their reconcilability. Section 1 considers the architectonic legislator in light of broader Greek assumptions regarding foundational law-making. Section 2 then turns to the status of law-making expertise as a part of political science and examines the mode of practical reason exercised by the legislative founder. Finally, in section 3, and building on recent interpretations which have emphasised that Aristotle operates with an extended teleological conception of nature, I argue that acts of legislative founding and nature can consistently serve as joint causes of the polis because the ‘products’ of the practical rationality of the legislator are themselves an expression of distinctly human nature.