Throughout his career Plato worried about the utility of Socrates' teaching method. A key difficulty with elenchus is that it concentrates on a proof of ignorance; its successful conclusion is the discovery that the answerer's thesis is wrong. It seems that elenchus cannot teach us what we should believe, but only eliminate one thing we should not. At his most playful, Socrates describes himself as one who has nothing to teach, who ‘neither knows nor thinks that he knows’, but only sets about to prove that all men share his ignorance. This prevalent scepticism in Plato's work was often attributed to the dialogue form in general. Boyle seems to have chosen the dialogue for The Sceptical Chymist: or Chymo-Physical Doubts & Paradoxes because it could best express his reservations about all chemical theory. And Dryden defends the form of his Of Dramatick Poesie as ‘Sceptical, according to the way of reasoning which was used by Socrates, Plato, and all the Academiques of old’. Much later Hurd argued that the dialogue should not be used to discuss important topics, such as religion, because of ‘the sceptical inconclusive air, which the decorum of polite dialogue demands’, while Hume reveals that he chose dialogue to express his thoughts on religion for this very reason: ‘Any question of philosophy … which is so obscure and uncertain, that human reason can reach no fixed determination with regard to it; if it should be treated at all; seems to lead us naturally into the style of dialogue and conversation.’