Pope from 1903-1914, during which time modern thinking was beginning to affect the church. Pius X was wary of reform. He believed stongly in the Catholic Church as an institution. He considered it disobedient for clergy and scholars to explore new explanations and approaches. People participating in these practices were called modernists, and many of them, including Alfred Loisy, and George Tyrell were excommunicated. It was not until Vatican II that the ideas of these scholars were accepted.

In 1907 Pius X published two decrees: Lamentabili, and Pascendi. Both were clear statements against modernity. In Pascendi, Pius X requires all bishops and seminary professors to take an oath against modernity. It also ecouraged censorship, which resulted in the formation of a secret society, the Sodalitium Pianum, which spied on suspected moderists.