The First Case of the Gateless Gate（無門関）
The Koan of One Letter of Nothingness （無字）or Zaoshou’s DOG（趙州狗子）
A monk asked Zaozhou, "Has a dog the Buddha Nature?"
Zaozhou replied, "NOTHINGNESS(無)"
The use of Koan is characteristic of the meditation training of Rinzai Zen. The role of the first case of Koan is similar to Catechism of the Roman Catholic Church. It is an indispensable part of the ceremony of initiation for the novice, who after the spiritual/bodily meditation exercise, must pass a series of examination (Koan) which Zen Master gives to him/her. There is a systematic way of Koan training in the Rinzai school of Zen, and the first case of Gateless Gate is often used as the first examination imposed upon Zen practitioners.
The young Nishida struggled with this test, but he did not pass the examination so easily, because he did not understand intellectually the purpose and meaning of the Koan “one letter of Nothingness.”
So he wrote a letter to Zen Mater Tekisui, asking many philosophical questions to the meaning and purpose of “One letter of Nothingness”. Tekisui wrote the following reply to Nishida, and Nishida, thinking much of this letter, put it in a frame, and kept it as his precious treasure for a long time.
