Hilde skips school to read Sophie's story, and she gets through the chapter on Berkeley. She finds herself agreeing with Alberto that her father has gone too far and then wonders whom she really agrees with, since her father wrote what Alberto said. Hilde thinks that she sees her reflection wink with both eyes. She finds out that her mom found her gold crucifix, and mentioned that fact to her father. However, when she asks for it, her mother cannot find it. Then she reads on in Sophie's World. Sophie wakes up on the morning of her birthday and convinces her mother that she is all right. Then she receives a call from Alberto, who has a plan. He thinks that they may somehow be able to influence what happens to them, because Hilde's father may not know what he is going to write until the moment that he writes it. He wants to figure out a way to somehow escape, but they cannot get away until Sophie has finished her course in philosophy. Hilde thinks that Alberto may have a point, because she knows her father will be writing quickly and that he might write something without realizing it. After school, on her way to meet Alberto at the major's cabin, Sophie gets a postcard from Hilde's father wishing her happy birthday. She also receives a postcard for Hilde that describes what Alberto will talk about in his next lecture and tells Hilde not to stay up too late reading.
Alberto describes the ##Enlightenment# Sophie and Hilde learn that the French Enlightenment was characterized by much "opposition to authority", politically as well as philosophically. The French thinkers had tremendous faith in reason. They wanted the masses to learn—to be enlightened—and they believed that this would result in great strides for humanity. They felt that we must return to a better, more natural way of living. They also wanted a natural religion, one that would be the same for all people. Finally, they felt that people had fundamental natural rights and they fought to see those rights upheld. Then a sea serpent appears in the lake and they go inside the cabin. Sophie finds a note for her and Hilde where the major points out that the UN is founded on principles from the Enlightenment. Hilde stops reading and goes downstairs to eat with her mother.
Hilde's father calls late that night to wish her a happy birthday, and she tells him she is very happy with his gift and that she thinks that Sophie and Alberto are real. Then she starts to read again. Alberto talks about Kant, who worked from the views of the empiricists and the rationalists. He believed that certain factors in our mind influence our experience of the world. We perceive everything as occurring in time and space, and these are innate characteristics of the human mind. Kant divides the world into things as they are in themselves and as we perceive them. We cannot know things as they are in themselves, but we can know how we perceive them. He felt that the law of causality was also a part of the human mind. Kant felt that we cannot know the answers to certain questions because they lie beyond human reason. He believed that these questions are answerable only through faith. Alberto is interrupted when Little Red Ridinghood knocks at the door and delivers another note from Hilde's father. Kant also believed that everyone has innate moral reason, and that moral actions are ones we perform out of a sense of duty. When we do so, we are free, because we are following our reason, which is a part of the world as it is in itself. Alberto also says that that Albert Knag cannot contradict reason, and that is their only weapon against him. Then Sophie leaves and meets Winnie-the-Pooh in the woods, who gives her a letter to Hilde that describes Kant's import for the UN.
When Hilde begins agreeing with Alberto that her father has gone too far, we are presented with a true paradox. Clearly, Alberto is a character in a book that Hilde's father has written. So agreeing with Alberto means agreeing with her father. But at the same time, Hilde's father is himself a character in that book, and his actions in the book are sometimes disagreeable to Hilde. Even Hilde cannot figure out what is really going on. However, she does know that more is happening than even her father understands. The gold crucifix and the scarf that Sophie found seem to have disappeared from Hilde's world, and this suggests that maybe Albert Knag has created more than he bargained for. He has really orchestrated the lessons that Alberto has given to Sophie and they are intended in his mind for Hilde, but the same lessons must be applied to his life as well. He created Sophie and Alberto's universe in his mind. But if it is true that Sophie cannot always trust herself or her mind, and that she is not always the same person from day to day, then it is also true of Albert Knag. Perhaps the point that Gaarder is making is that complete control is out of our reach. We cannot completely understand the world and, since our own minds are a part of that world, we therefore cannot entirely know our own mind. So Hilde's father, although he is the one writing about Alberto and Sophie, may not know exactly what he has done with them. Furthermore, the possibility, which Hilde is certain of, that Sophie and Alberto actually exist outside of the book, is one that cannot be ruled out.
We cannot rule out the possibility that Sophie and Alberto exist outside the book because we cannot know for sure that the characters do not exist somewhere else. After going through approximately 2000 years of philosophy, we have returned to one of its earliest truths—the only thing we can really know is that we know nothing. Socrates supposedly first stated this and Descartes said a similar thing centuries later. Now Gaarder may be using this statement to point out just how little we really do know. All of our lives may be inside a book that someone has written. The external world that we think we see may not actually have any physical substance. Perhaps there are other realities existing besides our own that we have no knowledge of. All we can really know is what both Descartes and Socrates knew—that we can question. Gaarder shows us that not only is it good for us to be philosophers, in a certain sense it is all we can ever hope to be. For certain knowledge can only be had, as Kant demonstrated, of what we perceive. And our perceptions need not tell us anything about the way things are in themselves. So, in a sense, flawed and prefigured as it is, our reason really is all that we have.