PREFACE So far as I know, no book is written on Zen in English or in any other European language, except 'The Sermons of a Buddhist Abbot,' by Shaku So-yen. Since its foundation some fourteen hundred years ago, no author in China or Japan has undertaken a systematic explanation of it, owing to the fact that it is believed to have a hidden meaning entirely beyond expression. Besides, there are difficulties which baffle every attempt of its expositors, because almost all the doctrinal works of old masters are metrical or enigmatical, and not only vague in meaning, but often mere jargon even to professional students. As for myself, I have stated the doctrine, so far as I understand it, in plainest language, avoiding its technical terms. I regret not a little that I have not been able to give in detail references to the books on which my exposition is based.