Toward the end of Feynman's life, his conservative view of quantum science became unfashionable. The fashionable theorists reject his dualistic picture of nature, with the classical world and the quantum world existing side by side. They believe that only the quantum world is real, and the classical world must be explained as some kind of illusion arising out of quantum processes. They disagree about the way in which quantum laws should be interpreted. Their basic problem is to explain how a world of quantum probabilities can generate the illusions of classical certainty that we experience in our daily lives. Their various interpretations of quantum theory lead to competing philosophical speculations about the role of the observer in the description of nature. Feynman had no patience for such speculations. He said that nature tells us that both the quantum world and the classical world exist and are real. We do not understand precisely how they fit together. According to Feynman, the road to understanding is not to argue about philosophy but to continue exploring the facts of nature.