In this as in many comedies, the theme of appearance vs. reality is key to the humour. Cases of characters and objects appearing to be something that they not actually are in reality, either through mistaken identity or through deliberate deceit, are very common in this play. Perhaps one of the first that are revealed to the audience is in Act I scene 2, when Tony deliberately tells Hastings and Marlow that the house he is sending them to is an inn and that his father-in-law is a character who is a member of the working class but who has ideas above his station. Note what Tony says for his reasons for doing this:
Father-in-law has been calling me whelp and hound this half-year. Now, if I pleased, I could be so revenged upon the old grumbletonian.
And revenged he certainly is, because Marlow and Hastings initially at least believe his lie completely, acting in ways that are very insulting to Mr. Hardcastle until they realise the truth. Appearance vs. reality of course is chiefly discussed in the relationship between Kate and Marlow, as Kate deliberately disguises herself as a maid in order to win Marlow's affection, and to make him less timid. Ironically, it is her disguise that brings out the reality of Marlow's true character. Appearances vs. reality is thus a key theme that is central to this comedy.