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How did Thomism become the official philosophy of the Roman Catholic Church in 1917?

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St. Thomas Aquinas St. Thomas Aquinas, from the *Demidoff Altarpiece*, tempera on poplar by Carlo Crivelli, 1476; in the National Gallery, London.

The establishment of Thomism as the official philosophy of the Roman Catholic Church was the culmination of a 19th-century revival movement that sought to defend the faith against modern idealist and subjectivist philosophies.1

This process was significantly advanced by Pope Leo XIII, who issued the encyclical Aeterni Patris in 1879. In this document, the Pope called for a restoration of the philosophy of the Church Fathers and Scholastics, specifically highlighting the work of St. Thomas Aquinas as a "special bulwark and glory of the Catholic Faith." Following this, Leo XIII named Aquinas the patron of all Catholic schools in 1880.1

The formal status of Thomism was solidified by the Code of Canon Law of 1917. This official compilation of church law mandated that all Catholic teachers of philosophy and religion follow the principles and methods of Aquinas, thereby establishing Thomism as the official philosophical framework of the Church.1