Fides et Ratio §54

⁵⁴ In our own century too the Magisterium has revisited the theme on a number of occasions, warning against the lure of rationalism. Here the pronouncements of Pope Saint Pius X are pertinent, stressing as they did that at the basis of Modernism were philosophical claims which were phenomenist, agnostic and immanentist. Nor can the importance of the Catholic rejection of Marxist philosophy and atheistic Communism be forgotten. Later, in his Encyclical Letter Humani Generis , Pope Pius XII warned against mistaken interpretations linked to evolutionism, existentialism and historicism. He made it clear that these theories had not been proposed and developed by theologians, but had their origins “outside the sheepfold of Christ”. He added, however, that errors of this kind should not simply be rejected but should be examined critically: “Catholic theologians and philosophers, whose grave duty it is to defend natural and supernatural truth and instill it in human hearts, cannot afford to ignore these more or less erroneous opinions. Rather they must come to understand these theories well, not only because diseases are properly treated only if rightly diagnosed and because even in these false theories some truth is found at times, but because in the end these theories provoke a more discriminating discussion and evaluation of philosophical and theological truths”. In accomplishing its specific task in service of the Roman Pontiff's universal Magisterium, the Congregation for the Doctrine of Faith has more recently had to intervene to re-emphasize the danger of an uncritical adoption by some liberation theologians of opinions and methods drawn from Marxism. In the past, then, the Magisterium has on different occasions and in different ways offered its discernment in philosophical matters. My revered Predecessors have thus made an invaluable contribution which must not be forgotten.