The Enlightenment” has been regarded as a turning point in the intellectual history of the West. The principles of religious tolerance, optimism about human progress and a demand for rational debate are often thought to be a powerful legacy of the ideas of Locke, Newton, Voltaire and Diderot. There was however a radical Enlightenment, indebted to the materialism of Hobbes and Spinoza, which posed an even greater challenge to traditional religious and political values. Given the ‘return of religion’ and the challenges of potential environmental catastrophe, Professor Champion argues to the contrary in this lecture on why we would be wise to go back to explore some of the more radical insights of Enlightenment freethinkers.