Four Foundations of Freedom.

"Public virtue cannot exist in a nation without private, and public virtue is the only foundation of republics." -John Adams

Public virtue is one of what the American Founders called the Four Foundations of Freedom. The Four Foundations of Freedom are, in order of importance according to most of the Founders:

Private Virtue
Public Virtue
Widespread Education
Auxiliary Precautions

The Founders consistently taught that, in the absence of these foundations, no society can survive, or at least maintain its freedom.

Private virtue means being a person of integrity; being honest in your dealings with others, being faithful in your duties to your family, controlling your appetites, etc.

Public virtue means to voluntarily sacrifice personal benefit for the good of society. For example, George Washington served two terms as President even when, as he was accepting the post, he wrote that it "would be the greatest sacrifice of my personal feelings and wishes that ever I have been called upon to make."

Contrary to our modern conception of education, widespread education to the Founders didn't mean job training; it meant classical, liberal education designed to teach individuals how to think, not what to think (Raed “A Thomas Jefferson Education” by Oliver DeMille).

And finally, auxiliary precautions are a society's forms of government that ideally protect life, liberty, property, and the pursuit of happiness. Auxiliary precautions include Legitimate Foundation, Legitimate Authority, Legitimate Role, Separation of Powers, Checks, Balances, Federalism, Written Constitution, Enumerated Limited Powers, Periodic Elections, Electoral College, and Fractionalization.