Mrs. Malaprop is certainly one of the most memorable characters in this play, and she has become so famous that she was used as the basis of a new word in the English language, a malapropism, which means to use a similar but incorrect word by mistake that creates a comic effect. This is certainly one of her roles throughout the entire play as she is doomed to try and adopt a formal register including more difficult vocabulary that, ironically, she wishes to show she can master, but only ends up mastering her. A classic example of this comes in Act I scene 2 when Mrs. Malaprop is talking about the education young women should receive and what they should and shouldn't be able to do:
I would have her instructed in geometry, that she might know something of the contagious countries; but above all, Sir Anthony, she should be mistress of orthodoxy, that she might not mis-spell, and mispronounce words so shamefully as girls usually do; and likewise that she might reprehend the true meaning for what she is saying.
The humour and irony is clear: Mrs. Malaprop, whilst saying that what is most important in the education of young women is that they are able to express themselves clearly without confusion, actually shows her complete inability to do that which she feels is so important. Sheridan therefore uses the character of Mrs. Malaprop in this play to mock social customs through presenting the hypocrisy of society and how appearances are so much more important than the reality to the people of his day.