Some would disagree. And his analogy about piano music completely misses the possibility of improvisation and composition, making robots of us all. Besides, the sheet music is external to the piano, and it can be replaced with another song if desired. And pianos don't grow and learn and hurt, like people . . . Analogies can be helpful to illustrate a point, but propping up a bald assertion with an analogy alone can backfire.
Science observes the material world, but religion sees the mental, nonmaterial.
If there is a God, Lewis argues, then God is much more like mind than anything else, and if this God is to communicate with us it will be more likely that he will do so through our minds, not through the material world. So, according to Lewis, if you want to find God, look within yourself to discover this urging to morality and realize that you have broken this law, every day. Lewis does not address situational ethics in this book, though it would seem relevant. In fact, Lewis is confident that his readers will be tacitly convinced of the correctness of this line of thinking. And Lewis can afford to relax, I think, because most of his readers are Christians who buy the book because they are looking for substantiation.