The essay aims to analyze the figure of the priest and missionary Giovanni Battista Sidoti in contrast with that of Arai Hakuseki, a Confucian scholar and politician, and also a scholar of the Tokugawa dynasty. The comparison and intellectual debate that followed took place in the first decades of the 18th century, a historical period that saw the decline and difficulties of the Catholic missions and at the same time a timid opening up of Japanese politics and of the cultural-scientific world towards the West.