True Name

A true name is a word or group of words in the Ancient Language which represented a person's true self.

Overview
Since the Ancient Language allows for objects to be controlled through their names, the knowledge of one's true name is a source of great power. Brom warned Eragon that if another person learned his true name, he could be controlled by that person.

When Oromis promised to teach Eragon everything he could concerning any one branch of magic, Eragon asked if Oromis could teach him his true name. Oromis admitted that he likely could, but denied the request, telling him that "a person must earn enlightenment." He stated that while a true name could be of great importance magically, it was not a spell in and of itself and therefore exempt from his promise.

It was revealed in Brisingr that a person's true name can be changed, and in doing so a person gains freedom from all past commitments he/she made in the Ancient Language. In other words, if a person were to promise something in the Ancient Language, and his/her true name changes at a later date, then the promises no longer hold them since he/she is essentially not the person who made the promise anymore. In order for one's true name to change, their personality has to change in some significant manner. For example, Oromis stated that becoming a mother and meeting Brom altered Selena to such a degree that her true name changed. The power of a true name is strong, stronger than even the Rider-Dragon bond.

All elves instinctively know their true names.