Why did Oliver Goldsmith use the theme of reality vs appearance in She Stoops to Conquer?
In order to effectively convey upon the audience the overall sense of confusion and disorder that is evident mostly in Marlow as the leading character, Goldsmith utilizes the comedic vehicle of reality versus appearance as with the purpose of keeping the interest of the audience.
The convoluted personality of Marlow clashes with the secure demeanor of Kate. This, in itself, propels the opportunity for Kate to test her wits as well as to test her future husband's gullible nature. Altogether it works in tandem: Kate pretends to be a maid in order to ease Marlow's nervous reaction to upper-class women. Conversely, Marlow shows his ability to control his weaknesses, albeit with a lot of difficulty, which impresses Kate and solidifies their impending romance.
MARLOW. (Aside.) This simplicity bewitches me, so that if I stay, I'm undone. I must make one bold effort, and leave her. (To her.) Your partiality in my favour, my dear, touches me most sensibly: and were I to live for myself alone, I could easily fix my choice...Farewell. [Exit.]
The use of contrasting circumstances as the journey towards a happy ending is ultimately what the comedic playwright would prefer to use to denote how a seemingly "everyday" couple (of their time) would find love and end up liking each other despite of it all.
MISS HARDCASTLE. I never knew half his merit till now. He shall not go, if I have power or art to detain him. I'll still preserve the character in which I STOOPED TO CONQUER; but will undeceive my papa, who perhaps may laugh him out of his resolution.