Nagel says that moving from appearance to reality makes no sense regarding the subjective character of experience. What does he mean, and why does he say that?
There is a saying that goes along the lines of “a man is little more than the sum of his experiences.” In other words, life is a constant series of relations and interrelations between people and events. Throughout a person’s lifetime, the experiences derived from these relationships will create the essence of the belief system that a person will prescribe. If time could be re-written and different variants on a person’s life experience were designed, it is not inconceivable that the end result would be a totally different person, as the person’s core value system or ideologies could have been altered in the revision process.
A great deal of Nagel’s thought process revolved around the belief that the reality of a human being (or a human being’s perception of reality) was based exclusively on experience. That is, those things that the individual does that comprise the totality of his life will provide the basis for what a person understands as things that are real.
There is a misnomer that some prescribe to that a person can create a reality out of any “appearance” by way of imitating something else, but such a reality is dubious as there is no basis in actual experience. Nagel uses the example of a bat as a means of illustrating this point. That is, a person may imagine his is a bat, but he can never match the reality of being a bat because he has not experienced the life that a bat exists. Hence, any perceived reality from experience that is pure imaginative in origin is truly not reality at all. Instead, all that would exist would be a perceived reality that can never truly duplicate the essence of what actual is. Therefore, the meaning derived from such imitation is dubious and suspect at best.
Alter, Torin. (2002) Nagel on Imagination and Physicalism. 2 December 2006