Too many Westerners interested in Japanese Zen assume that the work on riddles, called koans, is its principal way. This is not so. It is not accepted or practised by the other important branch of Zen, the Soto. The non-logical koan method is not recommended for those on a philosophical path and does not ally harmoniously with it.
-- Notebooks Category 15: The Orient > Chapter 3: China, Japan, Tibet > # 157