Sophie goes into her hiding place and finds another letter there. It is a response to her own, and she learns that Alberto Knox is the name of the philosopher who is communicating with her and that he will send his letters via a messenger. He also mentions that she may come across a silk scarf that belongs to someone else and that she should take care of it. Sophie is bewildered because the letter was delivered directly to a secret spot and she cannot comprehend the connection between the philosopher and Hilde Møller Knag. She gets the next package, delivered directly to her by a Labrador, Alberto's messenger. The letter in the package tells her the dog's name is Hermes. Sophie learns about skepticism, the belief that we cannot have true knowledge about the world, practiced by the Stoics in Athens. Then she learns of Socrates, who lived in Athens and spent his time conversing with people throughout the city. What we know of him comes from the writings of his pupil, Plato. Socrates would ask questions in an attempt to get people to come to proper philosophical conclusions on their own. He was considered subversive and condemned to die, and, rather than appeal for mercy or flee Socrates drank hemlock and died. Socrates believed in principles that he upheld. He knew that he did not know very much, and this made him much smarter than other people. Socrates had faith in human reason and believed that people were only happy when they acted according to their reason. Therefore, if someone knows what the right thing to do is in a situation she will do it, because it will make her happy. Socrates did not believe that people would deliberately act in a way to make themselves unhappy. Sophie gets into another discussion with her mother after reading the letter, but her mother seems quite unreceptive to these ideas.


Sophie receives a videotape that evening and she is amazed to see that it contains Alberto in Athens. He tells her all about the way the city used to be and how Socrates would talk to people who went by, and then, somehow, he takes her back to ancient Athens. Alberto speaks to Socrates and Plato, and then Plato gives her a few questions to think about. Sophie is astounded by the videotape and cannot figure out what is going on.


The next day, Sophie thinks about the questions that Plato gave her, and when she receives a letter describing his philosophy, she learns that they are central to his thought. Plato set up a school, called the Academy, and much of his work is preserved. He believed that everything in nature changes, but that there is an eternal world of ideas outside of the natural world. Plato thought that each thing that we see is an approximation of some perfect idea that exists somewhere else. We cannot have true knowledge about things that change, so we cannot actually know the real world, but we can have true knowledge about things that we perceive through our reason. Thus Plato was very fond of mathematics, because it involves solely the use of reason. Plato believed that people were made up of a body that is a part of the natural world but also an immortal soul that is in contact with the world of ideas. When we are born, our soul no longer has the knowledge of that world, but through experience we jog its memory and recollect the true and perfect ideas. Plato suggested a few ways of ordering human civilization, based upon ruling through reason, and he believed that women were just as capable of reasoning as men.


The philosopher presents Socrates as a man of principle, because he was willing to die for what he believed in. We often consider the true test of someone's belief to be the risk that they will undergo in upholding it. However, what is interesting is that Socrates was killed by his own state. Although he stood for the use of human reason, some people found him so subversive to their own aims that they had him killed. But the murder of a man who simply asked questions demonstrates that Athens, although a center of learning, attempted to control the thoughts of its citizens. Philosophers and intellectuals of the past two thousand years have perceived Socrates as a great and noble thinker, but in his own time, this was not the common perception. If, as Alberto Knox suggests to Sophie, it is the nature of a philosopher to question the thoughts and actions of his contemporaries and to challenge the status quo, then they will always face persecution. Some states will take action against criticism, because many political systems do not allow themselves to be critiqued. Therefore, the philosopher in reality has two roles to play. One of them involves the individual use of reason to look at the great questions that will always be out there. The second role involves interaction with others in order to attempt to get other people to think beyond the routines of their daily lives and contemplate the questions we cannot answer. The second role can be dangerous, because both the government as well as the people themselves may not want to hear what a philosopher has to say. Gaarder seems to be suggesting, through Alberto Knox, that sacrificing one's life for one's principles is the right thing for a philosopher to do.

Plato returns to the idea of change. Socrates was concerned with moral philosophy and human interaction, and Plato attempted to unify a theory of the natural world with one of humanity. Plato was Socrates' pupil, and so clearly much of his work was influenced by Socrates. Alberto teaches Sophie about each philosopher, and he does so in a chronological manner, but she still takes the philosophy of each as a separate entity. Philosophy definitely builds upon itself, but it is important not to forget that each philosopher is an individual thinker capable of coming up with unique ideas. Of course, the pre-Socratics could not have responded to Socrates' ideas, and so one's time period does play a role, but that role is not total. Plato would not have been the great philosopher that he was if he had not been taught by Socrates, but his education did not make his ideas inevitable. The history of philosophy that Sophie learns about is not necessarily an additive history. Thinkers use and respond to the ideas of those before them, but this does not mean they are following some necessary progression in the history of thought.