Arya is avoiding Eragon, so he is unable to apologize. Instead, he throws himself into his studies, learning the way the elves imbue objects with energy, along with lessons in history, science, and culture. He also continues sparring with Vanir, who one day provokes Eragon to attack him magically. Vanir, to Eragon’s surprise, is able to defend himself without speaking; after he repels Eragon’s attack, he explains that he dislikes Eragon because he considers himself unworthy to be a Rider and unlikely to be able to defeat Galbatorix.
Oromis explains that Vanir was able to use magic without speaking because magic resides in thoughts rather than sounds, but is practiced through words for better control. In the wake of a terrible accident, an ancient race called the Grey Folk are said to have changed the nature of magic so that it could be constrained and controlled by language if spoken aloud; they also endowed the ancient language with the properties that it requires speakers to tell the truth and is able to describe the true nature of things.
The more Eragon studies and exercises, the worse and more frequent his seizures become until he is dominated by pain and the fear of pain. He nicknames his pain the Obliterator because it drives all other thoughts from his mind.