"According to the philosophy of Zen, we are too much a slave to the conventional way of thinking. which is dualistic through and through. No "interpenetration" is allowed, there takes place no fusing of opposites in our everyday logic. What belongs to God is not of this world, and what is of this world is incompatible with the divine. Black is not white, and white is not black. Tiger is tiger, and cat is cat, and they will never be one. Water flows, a mountain towers. This is the way things or ideas go in this universe of the senses and syllogisms. Zen, however, upsets this scheme of thought and substitutes a new one in which there exists no logic, no dualistic arrangement of ideas. We believe in dualism chiefly because of our traditional training. Whether ideas really correspond to facts is another matter requiring a special investigation. Ordinarily we do not inquire into the matter, we just accept what is instilled into our minds; for to accept is more convenient and practical, and life is to a certain extent, though not in reality, made thereby easier. We are in nature conservatives, not because we are lazy, but because we like repose and peace, even superficially. But the time comes when traditional logic holds true no more, for we begin to feel contradictions and splits and consequently spiritual anguish.
We lose trustful repose which we experienced when we blindly followed the traditional ways of thinking. Eckhart says that we are all seeking repose whether consciously or not just as the stone cannot cease moving until it touches the earth. Evidently the repose we seemed to enjoy before we were awakened to the contradictions involved in our logic was not the real one, the stone has kept moving down toward the ground. Where then is the ground of non-dualism on which the soul can be really and truthfully tranquil and blessed? To quote Echart again, "Simple people conceive that we are to see God as if He stood on that side and we on this. It is not so; God and I are one in the act of my perceiving Him." In this absolute oneness of things Zen establishes the foundations of its philosophy. The idea of absolute oneness is not the exclusive possesion of Zen.
There are other religious and philosophies that preach the same doctrine. If Zen, like other monisms or theisms, merely laid down this principle and did not have anythng specifically to be known as Zen, it would have long ceased to exist as such. But there is in Zen something unique which makes up its life and justifies its claim to be the most precious heritage of Eastern culture. The following "Mondo" or dialogue (literally questioning and answering) will give us a glimsp into the ways of Zen, A monk asked Joshu, one of the greatest masters in China, "What is the ultimate word of Truth?" Instead of giving him any specific answer he made a simple response saying, "Yes." The monk who naturally failed to see any sense in this kind of response asked for a second time, and to this the Master roared back. "I am not deaf!" See how irrelevantly (shall I say) the all-important problem of absolute oneness or of the ultimate reason is treated here! But this is characteristic of Zen, this is where Zen transcends logic and overrides the tyranny and misrepresentation of ideas. As I have said before, Zen mistrusts the intellect, does not rely upon traditional and dualistic methods of reasoning, and handles problems after its own original manners....To understand all this, it is necessary that we should acquire a "third eye", as they say, and learn to look at things from a new point of view." ~DT Suzuki