chap 5 Back on This Side of the Door

The professor believes that the children need to be less judgmental and consider wider possibilities. When they are finished, the Professor, to their surprise, asks them why they are so certain that Lucy's story isn't true. He asks them to consider their own past experiences. Who, he asks, is more truthful: Lucy, or Edmund? He then advises them to use logic, lamenting, "Why don't they teach logic at these schools?" Logically, he says, Lucy is either telling lies, going mad, or telling the truth. He concludes that since Lucy is not a liar, and is not going mad, she must therefore be telling the truth.