The balance of powers saved Sparta, while the excess of tyranny in Persia and the excess of liberty at Athens have been the ruin of both...This discourse on politics is suddenly discovered to have an immediate practical use; for Cleinias the Cretan is about to give laws to a new colony.
At the beginning of the fourth book, after enquiring into the circumstances and situation of the colony, the Athenian proceeds to make further reflections.

Chance, and God, and the skill of the legislator, all co-operate in the formation of states.

And the most favourable condition for the foundation of a new one is when the government is in the hands of a virtuous tyrant who has the good fortune to be the contemporary of a great legislator.

But a virtuous tyrant is a contradiction in terms; we can at best only hope to have magistrates who are the servants of reason and the law.

This leads to the enquiry, what is to be the polity of our new state.