Issues of human rights and freedoms always inflame passions, and John Rawls's A Theory of Justice will do the same. Published in 1971, it links the idea of social justice to a basic sense of fairness that recognizes human rights and freedoms. Controversially, though, it also accepts differences in the distribution of goods and services - as long as they benefit the worst off in society.

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.

Gordon W. Allport's 1954 book The Nature of Prejudice helped mold the ways in which psychologists investigate prejudice. But the American's work reached further than that, also helping to shape society as a whole and making a substantial contribution to the US Civil Rights Movement, as well as to the country's anti-discrimination and anti-segregation laws of the 1950s and 1960s.

Having witnessed some negative effects of democratic revolutions in his native France, Tocqueville visited America in 1831 to see what a functioning republic looked like. His main concerns were that democracy could make people too dependent on the state and that minority voices might not be heard - a problem he termed "the Tyranny of the Majority". By examining America thoroughly, Tocqueville hoped to show how a democratic system could avoid these pitfalls.

In Philosophical Investigations, the Austrian philosopher Ludwig Wittgenstein presents a radical approach to problems in the philosophy of language and the philosophy of mind. In fact, he sets out a radically new conception of philosophy itself. Published in 1953, two years after Wittgenstein's death, many still consider it one of the finest works of 20th century philosophy.