"How do you know that?"
"I got a letter from him."
"How do you know he wrote it?"
"It was signed with his name."
"Don't you think somebody might deceive you by signing his name to a letter?"
"Maybe."
"You never saw Tom Sawyer and never saw him write?"
"No, sir."
"And isn't it true that you don't know a thing about it?"
"I can't believe anybody would sign his name to a letter. Besides I wrote him one and it reached him, because this letter was his answer."