At the time, Buddhism was criticized by Confucian scholars and scholars of Japanese classical literature, and Entsu thought that the decline of Buddhism was caused by the development of astro-geography, and thus he mastered the study of the calendar of India.
当時は儒学者・国学者の間から仏教批判が起こり、円通は仏教の衰退は天文地理の研究から始まると考え、インドの暦学を修学した。