One of the only areas of separation between human abilities and Nature is Reason. The examples that Lewis uses to make this argument include the fact that understanding the operation of a machine is connected to that machine but is not a physical part of the machine. The frontier of the self involves the line between reason and the events which one encounters, whether they are physical or psychological in nature. This frontier only runs in one direction; the Reason that human generates is able to change Nature, but Nature cannot produce rational thoughts and use them to affect us. For example, the study of mathematics has enabled us to design and build bridges, changing the physical shape of Nature. The arguments we use in our own minds let us change our own emotions, changing psychological Nature. It is easier to make permanent changes to physical Nature than to psychological Nature, but it is possible to accomplish both. Nature can change the way that we think, but in non-rational ways; as Lewis argues, “a train of thought loses all rational credentials as soon as it can be shown to be wholly the result of non-rational causes” (Lewis 39). Nature can extinguish our rational thoughts, but it cannot produce rational thought on its own. As a result, it is not possible, in Lewis’ opinion, for Nature to produce a divine consciousness.
As a result, the relationship between Reason and Nature is more like a parent and child than a pair of siblings. The objects around us are evidence that Reason has been able to turn Nature according to its own purposes. Lewis uses the examples of the ceiling over us and the walls around us – natural items turned into manmade objects and used to provide shelter. He also talks about our own clean hands and trimmed fingernails; if people did not have the faculty of Nature, our hands and fingernails would look completely different. (Indeed, how long did it take over the course of human history for people to decide that bathing more often than once a week was important?) Furniture shows us how Reason has taken the trees and put them to our own use – as do books.
The desire for a naturalistic sort of religion rewards a lot of our inner impulses. Nature is beautiful – as it should be, given that it is God’s creation, God’s gift to us and source of glory for Himself. However, the simple fact that the beauty of Nature is divine in origin does not mean that Nature contains God. The fact that Reason can stand apart, away from and over Nature, is a vivid picture for the way in which God stands far apart from and above all of His creation. It is true that God decides to intervene in history for His own glory, but the fact that the Father can only show His creatures a brief vision of His own back, because to show more would be more than humans can comprehend, is frustrating to behold, but ultimately shows how much more complete life in God’s country will be.