A further result of this contemplation of the world as the great Void is that the work done by mentalistic study is advanced still further, for not only are the things experienced by the five senses seen to be only thoughts but the thoughts themselves are now seen to be the transient spume and spray flung out of seeming Emptiness. Thus there is a complete reorientation from thoughts to Thought. Instead of holding a single thought or scenes of ideas in perfect concentration, the practiser must now move away from all ideas altogether to that seeming emptiness in which they arise. And the latter, of course, is the pure, passive, undifferentiated mind-stuff out of which the separate ideas are produced. Here there is no knowing and discriminating between one idea and another, no stirring into consciousness of this and that, but rather a sublime vacancy. For the Mind-essence is not something which we can picture to ourselves; it is utterly formless. It is as empty and as ungraspable as space.
-- Notebooks Category 23: Advanced Contemplation > Chapter 8: The Void As Contemplative Experience > # 115