AA's Big Book calls alcoholism "an illness which only a spiritual experience will conquer." Ernest Kurtz says this is "The closest the book Alcoholics Anonymous comes to a definition of alcoholism." Somewhat divergently in his introduction to The Big Book, non-member and early benefactor William Silkworth said those unable to moderate their drinking suffer from an allergy. In presenting the doctor's postulate, AA said "The doctor's theory that we have an allergy to alcohol interests us. As laymen, our opinion as to its soundness may, of course, mean little. But as ex-problem drinkers, we can say that his explanation makes good sense. It explains many things for which we cannot otherwise account." AA later acknowledged that "alcoholism is not a true allergy, the experts now inform us." Wilson explained in 1960 why AA had refrained from using the term "disease":