Philosophy (skill)
The training of the mind in a logical, orderly manner has been shown to be a very effective way of defending yourself from psychic damage. As you progress in the skill, your resistance to psychic attacks will increase. You'll also notice that your willpower recovers more quickly as your skill in philosophy rises.
Transcendent users of philosophy gain the benefit of CLARITY, a skill which allows limited protection from skills which will force the player to act against his or her will. This ability has a large willpower drain associated with it.