As long as there is duality, one sees "the other," one hears "the other," one smells "the other," one speaks to "the other," one thinks of "the other," one knows "the other"; but when for the illumined soul the all is dissolved in the Self, who is there to be seen by whom, who is there to be smelled by whom, who is there to be heard by whom, who is there to be spoken to by whom, who is there to be thought of by whom, who is there to be known by whom? Ah, Maitreyi, my beloved, the Intelligence which reveals all--by what shall it be revealed? By whom shall the Knower be known? The Self is described as "not this, not that" (neti, neti). It is incomprehensible, for it cannot be comprehended; undecaying, for it never decays; unattached, for it never attaches itself; unbound, for it is never bound. By whom, O my beloved, shall the Knower be known?

(The Upanishads)