“One has only to look at her and talk to her to see that she is not mad.”
“But then,” said Susan, and stopped. She had never dreamed that a grown-up would talk like the Professor and didn’t know what to think.
“Logic!” said the Professor half to himself. “Why don’t they teach logic at these schools? There are only three possibilities. Either your sister is telling lies, or she is mad, or she is telling the truth. You know she doesn’t tell lies and it is obvious that she is not ma. For the moment then and unless any further evidence turns up, we must assume that she is telling the truth.”
Susan looked at him very hard and was quite sure from the expression on his face that he was not making fun of them.”