Eragon tried to put his hand on the bay like Brom had, but it shied away. He automatically reached out with his mind to reassure the horse […] The contact was not clear or sharp like it was with Saphira, but he could communicate with the bay to a limited degree. (16.71)
"But what does that have to do with magic?" interrupted Eragon.
"Everything! It is the basis for all power. The language describes the true nature of things, not the superficial aspects that everyone sees." (19.49-50)
"While speaking [the magical language], it's impossible to practice deceit." (20.24)