From Pope St. John Paul II’s encyclical Fides et Ratio (1984):
This truth, which God reveals to us in Jesus Christ, is not opposed to the truths which philosophy perceives. On the contrary, the two modes of knowledge lead to truth in all its fullness. The unity of truth is a fundamental premise of human reasoning, as the principle of non-contradiction makes clear. Revelation renders this unity certain, showing that the God of creation is also the God of salvation history. It is the one and the same God who establishes and guarantees the intelligibility and reasonableness of the natural order of things upon which scientists confidently depend,29 and who reveals himself as the Father of our Lord Jesus Christ. This unity of truth, natural and revealed, is embodied in a living and personal way in Christ, as the Apostle reminds us: “Truth is in Jesus” (cf. Eph 4:21; Col 1:15-20). He is the eternal Word in whom all things were created, and he is the incarnate Word who in his entire person30 reveals the Father (cf. Jn 1:14, 18). What human reason seeks “without knowing it” (cf. Acts 17:23) can be found only through Christ: what is revealed in him is “the full truth” (cf. Jn 1:14-16) of everything which was created in him and through him and which therefore in him finds its fulfilment (cf. Col 1:17).
On the basis of these broad considerations, we must now explore more directly the relationship between revealed truth and philosophy. This relationship imposes a twofold consideration, since the truth conferred by Revelation is a truth to be understood in the light of reason. It is this duality alone which allows us to specify correctly the relationship between revealed truth and philosophical learning. First, then, let us consider the links between faith and philosophy in the course of history. From this, certain principles will emerge as useful reference-points in the attempt to establish the correct link between the two orders of knowledge.
29 “[Galileo] declared explicitly that the two truths, of faith and of science, can never contradict each other, ‘Sacred Scripture and the natural world proceeding equally from the divine Word, the first as dictated by the Holy Spirit, the second as a very faithful executor of the commands of God’, as he wrote in his letter to Father Benedetto Castelli on 21 December 1613. The Second Vatican Council says the same thing, even adopting similar language in its teaching: ‘Methodical research, in all realms of knowledge, if it respects . . . moral norms, will never be genuinely opposed to faith: the reality of the world and of faith have their origin in the same God’ (Gaudium et Spes, 36). Galileo sensed in his scientific research the presence of the Creator who, stirring in the depths of his spirit, stimulated him, anticipating and assisting his intuitions”: John Paul II, Address to the Pontifical Academy of Sciences (10 November 1979): Insegnamenti, II, 2 (1979), 1111-1112.
30 Cf. Second Vatican Ecumenical Council, Dogmatic Constitution on Divine Revelation, Dei Verbum, 4.
— Fides et Ratio 34-35