"According to Berkeley, my own soul can be the cause of my own ideas—just as when I dream—but only another will or spirit can be the cause of the ideas that make up the 'corporeal' world. Everything is due to that spirit which is the cause of 'everything in everything' and which 'all things consist in,' he said."
A little more than halfway through the story Alberto explains to Sophie about Berkeley's philosophy. Berkeley's idea is not necessarily any more enthralling or brilliant than any of the other philosophers who are discussed in the book. However, it just so happens that Berkeley is right in the case of Alberto and Sophie. They exist in the mind of Albert Knag, who created them in order to give his daughter a spectacular birthday gift. The point is not so much that Berkeley was right but rather a magnificent demonstration of just how relevant philosophy can be to our everyday lives. We must not only be philosophers, but we must also study philosophy, because it is possible that a previous thinker came up with a solution to something that is important to us. Furthermore, even if we do not get an answer from the thinkers of the past, seeing other ideas is a great way to stimulate new ones.