Once upon a time Freddie Mercury sang that, above all else, he wanted to break free. Many of us empathize. Freedom and liberty are such appealing principles that vastly different governments claim to embody them and partisans accuse rivals of imperiling them.

For many centuries the conventional wisdom held that liberals were the paradigmatic champions of liberty. From Mary Wollstonecraft and J. S. Mill to John Rawls, all of liberalism’s major philosophers made liberty central to their moral outlook. The United States presents itself as the leader of the “free” world, opposed to tyranny and autocracy. In the blunt words of the late philosopher Maurice Cranston, “By definition a liberal is a man who believes in liberty.”

But the ubiquity of this association has obscured alternative understandings of liberty. One of the most important springs from the republican tradition, which had a profound influence across antiquity and, directly or indirectly, shaped the thinking of figures as diverse as Hugo Grotius and Karl Marx. Yet by the twentieth century it was virtually a forgotten tradition, recovered only in the 1990s through the pioneering work of philosophers Philip Pettit and Quentin Skinner.