§ 57. We cannot know things in themselves, that is, things as they are apart from being experienced. However, things in themselves may exist and there may be other ways of knowing them, apart from our experience. We must guard against assuming that the limits of our reason are the limits of the possibility of things in themselves. To do this, we must determine the boundary of the use of our reason. We want to know about the soul. We want to know about the size and origin of the world, and whether we have free will. We want to know about a Supreme Being. Our reason must stay within the boundary of appearances but it assumes that there can be knowledge of the things–in–themselves that exist beyond that boundary. Mathematics and natural science stay within the boundary of appearances and have no need to go beyond. The nature of reason is that it wants to go beyond appearances and wants to know the basis of appearances. Reason never stops asking "why?." Reason won't rest until it knows the complete condition for the whole series of conditions. Complete conditions are thought of as being the transcendental Ideas of the immaterial Soul, the whole world, and the Supreme Being. In order to think about these beings of mere thought, we symbolically attribute sensuous properties to them. In this way, the Ideas mark the bounds of human reason. They exist at the boundary because we speak and think about them as if they possess the properties of both appearances and things–in–themselves.