Schopenhauer was just 30 when his magnum opus, Die Welt als Wille und Vorstellung, a work of considerable learning and innovation of thought, first appeared in 1818.

Much to his chagrin and puzzlement (so convinced was he of its merits), it didn't have an immediate effect on European philosophy, views and culture. It was only decades later that it was recognised as one of the major intellectual landmarks of the 19th century.

Epictetus, a Greek stoic and freed slave, ran a thriving philosophy school in Nicropolis in the early second century AD. His animated discussions were celebrated for their rhetorical wizardry and were written down by Arrian, his most famous pupil. Together with the Enchiridion, a manual of his main ideas, and the fragments collected here, The Discourses argue that happiness lies in learning to perceive exactly what is in our power to change and what is not, and in embracing our fate to live in harmony with god and nature.

One of the most influential works of this century, The Myth of Sisyphus and Other Essays is a crucial exposition of existentialist thought. Influenced by works such as Don Juan and the novels of Kafka, these essays begin with a meditation on suicide; the question of living or not living in a universe devoid of order or meaning.

The foundation for all modern economic thought and political economy, The Wealth of Nations is the magnum opus of Scottish economist Adam Smith, who introduces the world to the very idea of economics and capitalism in the modern sense of the words.

The Decline of the West - Volume 1 published in 1917, Volume 2 in 1922 - has exercised and challenged opinion ever since. It was a huge undertaking by Oswald Spengler (1880-1936), formerly an unpublished historian and philosopher who set out to radically reconsider history - the rise and fall of world civilisations and their cultures. His primary view was to reject the established Eurocentric paradigm (ancient/classical, Medieval - and, following the Renaissance - modern) and to take a totally new perspective.