By 1900 Catholic scholars in France, England, Italy and Germany were applying to the Bible and to church history the same historical and critical methods being used on every other ancient text, and some of them were drawing conclusions about the development of doctrine, the authorship of the gospels and the nature of revelation that could not easily be squared with the teaching of the schools. Pius X judged the tendency to be not a set of separate errors but one coherent system, and in 1907 he attacked it twice: the decree Lamentabili Sane Exitu listed sixty-five condemned propositions, and the encyclical Pascendi Dominici Gregis described the system, named it Modernism, and called it the synthesis of all heresies.
The enforcement went further than the documents. In 1910 the motu proprio Sacrorum Antistitum required every priest, before ordination and before taking up a teaching or pastoral office, to swear an oath against Modernist propositions, a requirement that stood until 1967. Diocesan vigilance committees were established to watch for suspect teaching, and an unofficial network known as the Sodalitium Pianum gathered denunciations, including against bishops and cardinals, in a manner that Benedict XV moved to suppress after Pius X's death.
Assessments remain sharply divided. Defenders point out that some of what was condemned was genuinely incompatible with Christian claims about revelation, and that the pope was defending believers rather than punishing scholars. Critics count the careers ended, the biblical scholarship driven out of Catholic institutions for two generations, and the atmosphere of suspicion, and argue that the questions were not answered but postponed until the Second Vatican Council had to take them up again.