Noam Chomsky is one of the world's most prominent and controversial public intellectuals. He is an internationally renowned professor of linguistics, but he is also a longstanding critic of US foreign policy and the influence of big business over the US government. When he published his first political critique 40 years ago, he was fired up by the war in Vietnam. Today he is still highlighting America's malign influence and calls the war in Afghanistan 'immoral'. He talks to Stephen Sackur.