Jack says that anyone placed in the position of legal guardian must have moral views about everything, and since the utmost morality doesn’t bring great happiness, he has always pretended to have a troublesome younger brother named Ernest who lives at the Albany Hotel and who frequently gets in trouble. This false brother gives Jack an excuse to go to town whenever he wants to.
Algernon counters by telling Jack a secret of his own. Just as Jack has invented a younger brother so as to be able to escape to London, Algernon has invented a friend called Bunbury, a permanent invalid whose sudden and frequent relapses afford him a chance to get away to the country whenever he wants. Bunbury’s illness, for instance, will allow Algernon to have dinner with Jack that evening, despite the fact that he has been committed, for over a week, to dining at Lady Bracknell’s. Algernon wants to explain the rules of “Bunburying” to Jack, but Jack denies being a “Bunburyist.” He says if Gwendolen accepts his marriage proposal he plans to kill off his imaginary brother, and that he’s thinking of doing so in any case because Cecily is taking too much interest in Ernest. Jack suggests that Algernon do the same with Bunbury. While the two men argue about the uses and merits of a married man’s “knowing Bunbury,” Lady Bracknell and Gwendolen are announced.