On 10 November 1619, Descartes had a dream and the world would never be the same again. Rene Descartes is most famous for his dictum cogito ergo sum, usually translated as ‘I think, therefore I am’. As often parodied as praised, the cogito has been the basis for numerous bad puns in cartoons, advertisements, T-shirts and coffee mugs. Despite many attempts to kill him off, Descartes and his ideas continue to haunt our world, 400 years on. Ergo is an irreverent romp through the life and thought of Descartes, exploring the relationship between the mind and the body, the self and the world, and reality and appearance. How can we know what is true, especially in our post-truth world?