" Magic is a kind of energy. It is given shape by human thoughts and emotions, by imagination. Thoughts define that shape—and words help to define those thoughts. That’s why wizards usually use words to help them with their spells. Words provide a sort of insulation as the energy of magic burns through a spell caster’s mind. If you use words that you’re too familiar with, words that are so close to your thoughts that you have trouble separating thought from word, that insulation is very thin. So most wizards use words from ancient languages they don’t know very well, or else they make up nonsense words and mentally attach their meanings to a particular effect. That way, a wizard’s mind has an extra layer of protection against magical energies coursing through it. But you can work magic without words, without insulation for your mind. If you’re not afraid of it hurting a little. "
― Jim Butcher , Fool Moon (The Dresden Files, #2)