On 4 August 1879, Pope Leo XIII issued the encyclical Aeterni Patris [Of the Eternal Father] which addressed the importance of authentically Christian philosophy and called for a increased attention to the works of St. Thomas Aquinas.
Leo believed that secular philosophy failed to lead people to the fullness of the truth – either by denying truth or at least by being unable to the highest truths which were known only by faith. Leo did not believe that faith and reason were opposed to one another but that reason needed and should lead one to faith. Authentic theology should, in turn, be based on philosophy.
While Leo noted the authentic relationship between faith and reason as expressed in the history of the Catholic Church, the foremost example of how theology should be done was reflected in the work of St. Thomas Aquinas. For this reason, Leo called for a return to a study of the scholastic theologians, especially Aquinas. It should, however, also be noted that Leo did not intend for philosophers or theologians to imitate Aquinas if, “there be anything that ill agrees with the discoveries of a later age, or, in a word, improbable in whatever way”.
Leo’s support of Aquinas contributed to the revival of Thomism at the end of the 19th and beginning of the 20th century and would influence the work of such philosophers and theologians as Karl Rahner, Bernard Lonergan, Jacques Maritain and Étienne Gilson.
One year later, on 4 August 1880, Leo would designate Aquinas the patron of all Catholic colleges, schools and universitis throughout the world.