your name isn't Jack at all; it is Ernest.
JACK: It isn't Ernest; it's Jack.
ALGERNON: You have always told me it was Ernest. I have introduced you to everyone as Ernest. You answer to the name of Ernest. You look as if your name was Ernest. You are the most earnest-looking person I ever saw in my life. It is perfectly absurd your saying that your name isn't Ernest. It's on your cards. Here is one of them.