Quote from Blood Of Elves 

"The earth which we tread. The fire which does not go out within it. The water from which all life is born and without which life is not possible. The air we breathe. It is enough to stretch out one's hand to master them, to subjugate them. Magic is everywhere. It is in air, in water, in earth and in fire. And it is behind the door which the Conjunction of the Spheres has closed on us. From there, from behind the closed door, magic sometimes extends its hand to us. For us. You know that, don't you? You have already felt the touch of that magic, the touch of the hand from behind that door. That touch filled you with fear. Such a touch fills everyone with fear. Because there is Chaos and Order, Good and Evil in all of us. But it is possible and necessary to control it. This has to be learnt. And you will learn it, Ciri."