Answer:
Irony
Explanation:
From the very title on Irony (the opposite of what the public expects) is the outstanding satirical tool: Being earnest is exactly what the main characters are lacking of. When Jack announces he is going to kill his imaginary brother Ernest, and suggest to Algernon he should do the same with the imaginary Bunbury, Algernon replies:
¨Nothing will induce me to part with Bunbury, and if you ever get married (with Algernon´s sister), which seems to me extremely problematic, you will be very glad to know Bunbury. A man who marries without knowing Bunbury has a very tedious time of it.¨
