Pope Leo XIII had sought to revive the inheritance of Thomas Aquinas, 'the marriage of reason and revelation', as a response to secular 'enlightenment'.
Under the pontificate of Pius X neo-Thomism became the blueprint for an approach to theology.
Perhaps the most controversial aspect of Pius X's papacy was his vigorous condemnation of what he termed 'Modernists', whom he regarded as dangers to the Catholic faith (see for example his oath against modernism).
He also encouraged the formation and efforts of Sodalitium Pianum (or League of Pius V), an anti-Modernist network of informants, which was seen negatively by many people, due to its accusations of heresy against people on the flimsiest evidence.
This campaign against Modernism was run by Umberto Benigni, in the Department of Extraordinary Affairs in the Secretariat of State, which distributed anti-Modernist propaganda and gathered information on "culprits".
Benigni had his own secret code – Pius X was known as Mama.

Pius X's attitude toward the Modernists was uncompromising.
Speaking of those who counseled compassion to the "culprits" he said: "They want them to be treated with oil, soap and caresses.
But they should be beaten with fists.
In a duel, you don't count or measure the blows, you strike as you can."

The movement was linked especially to certain Catholic French scholars such as Louis Duchesne, who questioned the belief that God acts in a direct way in the affairs of humanity, and Alfred Loisy, who denied that some parts of Scripture were literally rather than perhaps metaphorically true.
In contradiction to Thomas Aquinas they argued that there was an unbridgeable gap between natural and supernatural knowledge.
Its unwanted effects, from the traditional viewpoint, were relativism and scepticism.
Modernism and relativism, in terms of their presence in the church, were theological trends that tried to assimilate modern philosophers like Immanuel Kant as well as rationalism into Catholic theology.
Modernists argued that beliefs of the church have evolved throughout its history and continue to evolve Anti-Modernists viewed these notions as contrary to the dogmas and traditions of the Catholic Church.

In the decree, entitled Lamentabili sane exitu (or "A Lamentable Departure Indeed"), issued on 3 July 1907 by the Holy Office, Pius X formally condemned 65 propositions, mainly drawn from the works of Alfred Loisy and concerning the nature of the church, revelation, biblical exegesis, the sacraments, and the divinity of Christ.
That was followed by the encyclical Pascendi dominici gregis (or "Feeding the Lord's Flock"), which characterized Modernism as the "synthesis of all heresies."
Following these, Pius X ordered that all clerics take the Anti-Modernist oath, Sacrorum antistitum.
 Pius X's aggressive stance against Modernism caused some disruption within the church.
Although only about 40 clerics refused to take the oath, Catholic scholarship with Modernistic tendencies was substantially discouraged.
Theologians who wished to pursue lines of inquiry in line with Secularism, Modernism, or Relativism had to stop, or face conflict with the papacy, and possibly even excommunication.
Pope Leo XIII had sought to revive the inheritance of Thomas Aquinas, 'the marriage of reason and revelation', as a response to secular 'enlightenment'. Under the pontificate of Pius X neo-Thomism became the blueprint for an approach to theology. Perhaps the most controversial aspect of Pius X's papacy was his vigorous condemnation of what he termed 'Modernists', whom he regarded as dangers to the Catholic faith (see for example his oath against modernism). He also encouraged the formation and efforts of Sodalitium Pianum (or League of Pius V), an anti-Modernist network of informants, which was seen negatively by many people, due to its accusations of heresy against people on the flimsiest evidence. This campaign against Modernism was run by Umberto Benigni, in the Department of Extraordinary Affairs in the Secretariat of State, which distributed anti-Modernist propaganda and gathered information on "culprits". Benigni had his own secret code – Pius X was known as Mama.
Pius X's attitude toward the Modernists was uncompromising. Speaking of those who counseled compassion to the "culprits" he said: "They want them to be treated with oil, soap and caresses. But they should be beaten with fists. In a duel, you don't count or measure the blows, you strike as you can."
The movement was linked especially to certain Catholic French scholars such as Louis Duchesne, who questioned the belief that God acts in a direct way in the affairs of humanity, and Alfred Loisy, who denied that some parts of Scripture were literally rather than perhaps metaphorically true. In contradiction to Thomas Aquinas they argued that there was an unbridgeable gap between natural and supernatural knowledge. Its unwanted effects, from the traditional viewpoint, were relativism and scepticism. Modernism and relativism, in terms of their presence in the church, were theological trends that tried to assimilate modern philosophers like Immanuel Kant as well as rationalism into Catholic theology. Modernists argued that beliefs of the church have evolved throughout its history and continue to evolve Anti-Modernists viewed these notions as contrary to the dogmas and traditions of the Catholic Church.
In the decree, entitled Lamentabili sane exitu (or "A Lamentable Departure Indeed"), issued on 3 July 1907 by the Holy Office, Pius X formally condemned 65 propositions, mainly drawn from the works of Alfred Loisy and concerning the nature of the church, revelation, biblical exegesis, the sacraments, and the divinity of Christ. That was followed by the encyclical Pascendi dominici gregis (or "Feeding the Lord's Flock"), which characterized Modernism as the "synthesis of all heresies." Following these, Pius X ordered that all clerics take the Anti-Modernist oath, Sacrorum antistitum.  Pius X's aggressive stance against Modernism caused some disruption within the church. Although only about 40 clerics refused to take the oath, Catholic scholarship with Modernistic tendencies was substantially discouraged. Theologians who wished to pursue lines of inquiry in line with Secularism, Modernism, or Relativism had to stop, or face conflict with the papacy, and possibly even excommunication.
Pope Pius X