The evidence that the narrator provides for his claim that he is not mad can be found in the first two paragraph's of Poe's short story, "The Tell-Tale Heart." First, the narrator claims that if he was mad, he would not be able to tell the story so calmly. He also says that he was very, very nervous, but not mad. This nervousness caused him to have sharpened senses, as opposed to dull ones, and that he has a heightened sense of hearing, enabling him to hear all things in Heaven and Hell. In the second paragraph, the narrator says, "Madmen know nothing," but he calculated and executed the murder so well that he obviously knows quite a bit.
In Edgar Alan Poe's suspenseful short story "The Tell Tale Heart" the narrator opens the story by explaining why he knows he is not mad. He tries to convince his audience that he is not mad. He states the lines:
I heard all things in the heaven and in the earth. I heard many things in hell. How then am I mad? Hearken! and observe how healthily, how calmly, I can tell you the whole story.
He uses the reference of being able to tell the story accurately and in detail so that the reader will see that he has a clear head. If the facts are so clear in his mind, then he can not be mad. He believes that mad people would not have his level of recall.