“Intuitive insight is born out of inquiry. It is here that meaningful ‘questioning’ has to be raised. The nature of the question runs along the lines of “Who am I?” or “Who questions?” “All things are reducible to the one;what then is the one reducible to?” “What is the difference between ‘abiding mind’ and the ‘mind in activity’-is this one mind or two minds?””What observes the mind?” As a technique, the raising of such meaningful but paradoxical questions becomes a powerful tool for summoning great energy and focus. This is what Chinese Ch’an calls facing the ‘great doubt’ (da yiqing), in which the immediacy of the question is not unlike having one’s nose literally pressed up against the blank ‘iron wall’ of the inquiry. The key point of the YOGA OF NON-PROLIFERATION is to raise question in such a way as to directly introduce the mind to its own face.”