The Universe of Magic is in the mind of a man: the setting is but Illusion even to the thinker. Humanity is progressing; formerly men dwelt habitually in the exterior world; nothing less than giants and Paynim and men-at-arms and distressed ladies, vampires and succubi, could amuse them. Their magicians brought demons from the smoke of blood, and made gold from baser metals. In this they succeeded; the intelligent perceived that the gold and the lead were but shadows of thought. It became probable that the elements were but isomers of one element; matter was seen to be but a modification of mind, or (at least) that the two things matter and mind must be joined before either could be perceived. All knowledge comes through the senses, on the one hand; on the other, it is only through the senses that knowledge comes.