Ko means “vacant” or “void,” and ku means “air,” “space,” or “emptiness.” So koku means “space.” Space and time have been most important concepts in philosophy since ancient times, and even in ancient India people frequently discussed the problem of space and time. And this tradition influenced Buddhism, so the problem of space and time became very important in Buddhism in India. The tendency was also accepted by Chinese Buddhism, so there are many stories of Chinese Buddhist masters discussing space and time. In this chapter Master Dogen discusses space. He first quotes a discussion about space between Master Shakkyo Ezo and Master Seido Chizo. Then he gives his own explanation, quoting a poem by Master Tendo Nyojo, a discussion between Master Baso Do-itsu and a monk called Seizan Ryo, and the words of Master Vasumitra.