Karen Armstrong

 "It was only possible to define or comprehend something when there was duality. A person can see, taste, or smell something that is separate and apart from him- or herself. But when “the whole [brahman] has become a person’s very self [atman], then who is there for him to see and by what means? Who is there for me to think of and by what means?”14 It was impossible to perceive the perceiver within oneself. So you could only say neti . . . neti (“not this”). The sage affirmed the existence of the atman while at the same time denying that it bore any similarity to anything known by the senses.