Many schools of psychology have come and gone since Freud died. And yet he has a cultural legacy. What is that legacy?

The most important part of Freud's legacy is his influence on our language. We use terms—ego, repression, projection, neurosis, sibling rivalry, and Freudian slip—without realizing their source. In addition, his theories influence how we interpret human behavior—in history, literary criticism, biography, sociology, medicine, education, and ethics. We now take for granted that early life experiences influence how we think and feel and behave as adults. For example, before Freud, we had little awareness of the traumatic effects of child sexual abuse. Now we read of such cases every day. His influence is so profound, historians refer to the 20th century as "the century of Freud."

Would Lewis have agreed that childhood experiences influence us?

Yes. He was acutely aware of the influence of his early childhood, especially his mother's death when he was 9 years old. Lewis never fully recovered. In his autobiography, he writes extensively about both the positive and negative early experiences that shaped his life.

You write that "the early life experiences show striking parallelism." If those experiences of love and loss were so similar, why did these men turn out so different?

Until Lewis came to a personal faith, they were very much alike—gifted intellectually, introspective, highly critical and wary of others, clinically depressed, pessimistic, gloomy and hostile toward their fathers and toward all authority—especially to the notion of an Ultimate Authority, etc. Then, in his early 30s, Lewis had a conversion experience that transformed his life.