Buddhism in its course of development has completed a form which distinguishes itself from its so called primitive or original type – so greatly, indeed, that we are justified in emphasizing its historical division into two schools, Hinayana and Mahayana, or the Lesser Vehicle and the Greater Vehicle of salvation.
As a matter of fact, the Mahayana, with all its varied formulae, is no more than a developed form of Buddhism and traces back its final authority to its Indian founder, the great Buddha Sakyamuni. When this developed form of the Mahayana was introduced into China and then into Japan, it achieved further development in these countries. This achievement was no doubt due to the Chinese and Japanese Buddhist leaders, who knew how to apply the principles of their faith to the ever varying conditions of life and to the religious needs of the people. The fundamental ideas of the Mahayana are expounded in the Prajnaparmita group of Buddhist literature. In India two Mahayana schools are known : The Madhamika of Nagarjuna and Vijnaptimatra or Yagacara of Asanga and Vasubandhu. In China more schools developed : the Tenai, the Kegon, the Jodo, the Zen, etc. In Japan we have besides these the Hokke, the Shingon, the Shin, the Ji, etc. All of them belong to the Mahayana wing of Buddhism.
There are people who declare that this branch of Buddhism is in reality no Buddhism in the sense that the latter is commonly understood. My contention, however, is this: anything that has life in it is an organism, and it is in the very nature of an organism that it never remains in the same state of existence. An acorn is quite different, even as a young oak with tender leaves just out of its protective shell is quite different from a full grown tree so stately and gigantic and towering up to the sky. But throughout these varying phases of marks of identity, when we know that one and the same plant has passed through many stages of becoming. The so called primitive Buddhism is the seed, out of it Far-Eastern Buddhism has come into existence with the promise of sill further growth.
Among the many secs of Buddhism that have grown up, especially in China and Japan, we find a unique order claiming to transmit the essence and spirit of Buddhism directly from its author, and this is not through any secret document or by means of any mysterious rite. This order is one of the most significant aspects of Buddhism, not only from the point of view of its historical importance and spiritual vitality, but from the point of view of its most original and stimulating manner of demonstration. The “Doctrine of the Buddha-heart (buddhahridaya)” is its scholastic name, but more commonly it is known as “Zen”. That Zen is not the same as Dhyana, though the term Zen is derived from the Chinese transliteration (ch’an-na, zenna in Japanese) of the original Sanskrit.
This school is unique in various ways in the history of religion. Its doctrines, theoretically stated, may be said to be those of speculative mysticism, but they are presented and demonstrated in such a manner that only those initiates who, after long training, have actually gained an insight into the system can understand their ultimate signification. To those who have not acquired this penetrating knowledge, that is, to those who have not experienced Zen in their everyday active life- its teachings, or rather its utterances, assume quite a peculiar, uncouth and even enigmatical aspect. Such people, looking at Zen more or less conceptually consider Zen utterly absurd and ludicrous or deliberately making itself unintelligible in order to guard its apparent profundity against outside criticism. But simply because the human tongue is not an adequate organ for expressing the deepest truths of Zen, the latter cannot be made the subject of logical exposition; they are to be experienced in the inmost soul when they become for the first time intelligible. In point of fact, no plainer and more straightforward expressions than those of Zen have ever been made by any other branch of human experience. Coal is black- this is plain enough; but Zen protests, “Coal is not black”. This is also plain enough and indeed even plainer than the first positive statement when we come right down to the truth of the matter.
[ Excerpts from "An Introduction to Zen Buddhism" published in 1964 ]