A work that had a huge influence on great thinkers including celebrated German philosopher Immanuel Kant, An Enquiry is Hume's examination of how we obtain information and form beliefs. He argues that we mainly gain knowledge through our senses, a theory known as empiricism. But while the impressions from our senses are key to our beliefs about the world, Hume argues that reason and facts play only a limited part.

First published in 1651, Leviathan drove important discussions about where kings get their authority to rule and what those kings must, in turn, do for their people. This is known as the "social contract". Thomas Hobbes wrote the book while exiled from his native England following the English Civil War that unseated King Charles I. In the face of England's radical - if temporary - rejection of its monarchy, Hobbes wanted to explain why it was important to have a strong central government, which in his time meant having a sovereign at its head.

First available in 1689, John Locke's Two Treatises of Government is considered one of the most important works ever written on the foundations of government. Published anonymously, it argues against the popular idea at the time that monarchs have a God-given right to rule. Instead Locke proposes that sovereignty - supreme authority - ultimately resides with the people.

In her 1958 work, political theorist Hannah Arendt asks two fundamental questions: "Under what conditions do politics emerge?" and "Under what conditions can politics be eliminated?" In searching for answers she turns some long-established thinking on its head. Ancient political philosophers such as Plato and Aristotle believed that a life spent thinking was more important than an active life of labor, work, and action. But Arendt argues that political action is every bit as important as political thinking.

Some people think nationhood is as old as civilization itself. But for anthropologist, historian, and political scientist Benedict Anderson, nation and nationalism are products of the communication technology of the era known as the modern age, which began in 1500. After the invention of the printing press around 1440, common local languages gradually replaced Latin as the language of print. Ordinary people could now share ideas of their own.