Which phrase in the Constitution expresses the idea of self-government?

The phrase "We the People" is significant because it highlights the principle of self-government that is foundational to the Constitution. This phrase indicates that the authority of the government derives from the consent of the governed—the people themselves. It reinforces the idea that citizens have the power to shape their government and that the government's legitimacy comes from its obligation to serve the interests and will of the people.

The other phrases, while important, focus on specific functions or goals of the government. "To form a more perfect union" refers to the aim of improving the relationships among the states and creating a stronger federal government. "Ensure domestic tranquility" emphasizes the government's role in maintaining peace and order within the country, and "Provide for the common defense" addresses the responsibility of protecting the nation from external threats. Each of these is crucial for understanding the purpose and responsibilities of government, but they do not encapsulate the core concept of self-determination and governance by the people in the way that "We the People" does.