There is a celebrated passage in Boswell’s Life of Johnson where Boswell broached the subject of Bishop Berkeley’s idealist philosophy and his “ingenious sophistry to prove the non-existence of matter”. When he then suggested that the idea could not be refuted, Johnson moved rapidly to a nearby large stone and “struck his foot with mighty force” against it, till he rebounded from it. As he did so, he said, “I refute it thus.” When we read this passage, we are impressed with Johnson’s commonsense approach to things. His answer appeals to us because the notion that matter is an illusion…