In Federalist Paper No. 51, James Madison’s argument most clearly addresses which of the following principles of constitutional government?

In Federalist Paper No. 51, James Madison emphasizes the principle of checks and balances as a fundamental aspect of constitutional government. Madison argues that the structure of government must provide a way to control the powers of the different branches, thereby ensuring that no single branch becomes too powerful. This is achieved by establishing mechanisms that allow each branch to limit the powers of the others, creating a system where ambition counteracts ambition.

He highlights that each branch will strive to maintain its independence while also being accountable to the other branches, effectively maintaining a balance of power. This ensures that a strong government does not lead to tyranny. Thus, Madison's arguments directly illustrate how checks and balances function as a safeguard against the concentration of power, making it the most relevant principle addressed in this paper.

The other options, while important elements of constitutional governance, are not the central focus of Madison's argument in this particular paper. Federal structure pertains more to the distribution of power between state and federal levels, popular sovereignty relates to the authority of the government deriving from the consent of the governed, and individual rights emphasize the protections afforded to citizens, which are explored in other contexts within the Federalist Papers and in the Constitution itself.