John Gray talks to Matthew Sweet about why the Aztecs might have had a better understanding of freedom than we do and other human illusions about meaning and progress. Also we consider how artistic movements become successful as the National Gallery stages an exhibition devoted to Paul Durand-Ruel, the french art dealer who discovered the Impressionists. Matthew talks to National gallery curator Christopher Riopelle. Also Jacky Klein, art historian and Godfrey Barker, man of letters and art critic discuss the anthropology of the art world through time.