Sociologist Émile Durkheim's 1897 work On Suicide is a powerful evidence-based study of why people take their own lives. In the late 19th century it was generally accepted that each suicide was an individual phenomenon, caused by such personal factors as grief, loss, and financial problems. But Durkheim felt there were patterns in suicide rates, and believed that a more likely cause of suicide lay in the individual's relationship to society.

Western thinking about the Middle and Far East has been distorted by stereotype and inaccuracy. This argument lies at the center of Palestinian-American literary theorist Edward Said's groundbreaking book, Orientalism. Originally published in 1978, it cemented Said's reputation as the father of postcolonial studies.

In his 1807 work Phenomenology of Spirit, G. W. F. Hegel introduced the world to his philosophical system. His most influential work - and the culmination of the German Idealist movement begun in the late 18th century as a response to the works of Immanuel Kant - the book remains one of the undisputed classics of Western thought.

More than two centuries after its initial publication in 1781, Immanuel Kant's Critique of Pure Reason remains perhaps the most influential text in modern philosophy. Kant himself claimed his work as a revolutionary document and insisted that it changed the discipline of philosophy as thoroughly as Copernicus had changed astronomy 300 years earlier, when he said the Earth revolved around the sun and not the other way round.

Philosopher Judith Butler's 1990 work, Gender Trouble, shook the foundations of feminist theory and changed the conversation about gender. While many thinkers already accepted that "gender" was a category constructed by society rather than defined by one's genitalia, Butler went further and argued that gender is performative - it exists only in the acts that express it. Society determines that wearing makeup is "feminine" - but some men wear makeup. Are they "women"?