What darkness was the ‘Enlightenment’ supposed to have removed? The answer is irrational forms of religion. Most of the ‘enlightened’ took the view that revealed religion was irrational and that natural religion could be rational; but some were sceptical about natural religion too. Hume was the most honest and the most penetrating thinker of the latter group. His biographer, Professor E. C. Mossner, is not alone in believing that the Dialogues concerning Natural Religion is ‘his philosophical testament’.