It is a radical error which assails each one of us when we assume that we are individual knowers endowed with intellect and other means of knowledge which enable us to know objects. It is to dispel this inherent error that the Upanishads employ the unique metod known as adhyaropa-apavada, where word symbols used need not directly denote the self or Brahman but only serve to suggest what is not really characteristic of it, while the human mind naturally takes it to be such.
Brahman as the witnessing principle in us all, being of the very nature of consciousness, needs no extraneous means to know it. It has to be intuited by the self in itself as something devoid of all determining features, as the all in reality.
(From ‘ Contributions of Saccidanandendra to 20th Century Advaita’, by S. Raganath, 2005)