Few ideas have been as influential in the development of moral, political, legal, and economic thought in the broad Western tradition as the idea of natural law. It is also true that the understanding of natural law and its influence on specific norms and institutions—rights, justice, private property, rule of law, limited government—is not anywhere near as widespread in the 21st century as it was just 100 years ago. This book aims to help rectify this deficit by explaining the basic principles of natural law and highlighting significant contributions that key natural law scholars have made to ideas and concepts that have encouraged the growth of free societies.

The idea of natural law holds that all people, whatever their ethnicity, culture, or religion, can know the difference between good and evil, right and wrong. The idea, for example, of the Golden Rule—do unto others as you would have them do unto you—is understood as a principle of moral conduct that everyone can know. While such beliefs are applied to different and changing conditions and problems, the core principles always apply.

However, natural law is not a static tradition of thought. It has developed over time, partly through natural law theorists clarifying particular concepts, and partly through its proponents responding to ongoing intellectual challenges to its positions and changes in the realm of politics, society, and the economy. Whether it was the encounter between Europeans and the peoples of the New World in the late 15th century, or questions about what justice meant in the context of emerging market economies in the late 18th century, natural law scholars have applied natural law principles to discern how people should choose and act in these changing contexts.

While this book seeks to introduce listeners to how natural law thinkers have contributed to the enhancement of freedom in the political, legal, and economic realms, we will focus on some scholars more than others. These include individuals like Thomas Aquinas (1225-1274), Francisco Suárez, and Hugo Grotius, to name just a few.

Some focused their attention on very practical challenges arising from liberty of commerce within and across sovereign boundaries, while others explored the rights and obligations of individuals to each other as well as the state. All these endeavors helped to furnish an apparatus for thinking about the political, legal, and economic institutions necessary for promoting freedom and justice.