From Pope St. John Paul II’s encyclical Veritatis Splendor (1993):
Faced with this theory [of correct behavior being orientation rather than actions], one has to consider carefully the correct relationship existing between freedom and human nature, and in particular the place of the human body in questions of natural law.
A freedom which claims to be absolute ends up treating the human body as a raw datum, devoid of any meaning and moral values until freedom has shaped it in accordance with its design. Consequently, human nature and the body appear as presuppositions or preambles, materially necessary for freedom to make its choice, yet extrinsic to the person, the subject and the human act. Their functions would not be able to constitute reference points for moral decisions, because the finalities of these inclinations would be merely “physical” goods, called by some “pre-moral”. To refer to them, in order to find in them rational indications with regard to the order of morality, would be to expose oneself to the accusation of physicalism or biologism. In this way of thinking, the tension between freedom and a nature conceived of in a reductive way is resolved by a division within man himself.
This moral theory does not correspond to the truth about man and his freedom. It contradicts the Church’s teachings on the unity of the human person, whose rational soul is per se et essentialiter the form of his body.86 The spiritual and immortal soul is the principle of unity of the human being, whereby it exists as a whole — corpore et anima unus87 — as a person. These definitions not only point out that the body, which has been promised the resurrection, will also share in glory. They also remind us that reason and free will are linked with all the bodily and sense faculties. The person, including the body, is completely entrusted to himself, and it is in the unity of body and soul that the person is the subject of his own moral acts. The person, by the light of reason and the support of virtue, discovers in the body the anticipatory signs, the expression and the promise of the gift of self, in conformity with the wise plan of the Creator. It is in the light of the dignity of the human person — a dignity which must be affirmed for its own sake — that reason grasps the specific moral value of certain goods towards which the person is naturally inclined. And since the human person cannot be reduced to a freedom which is self-designing, but entails a particular spiritual and bodily structure, the primordial moral requirement of loving and respecting the person as an end and never as a mere means also implies, by its very nature, respect for certain fundamental goods, without which one would fall into relativism and arbitrariness.
86 Cf. Ecumenical Council of Vienne, Constitution Fidei Catholicæ: H. Denzinger-A Schönmetzer, Enchiridion Symbolorum Definitionum et Declarationum de Rebus Fidei et Morum [DS], 902; Fifth Lateran Ecumenical Council, Bull Apostolici Regiminis: DS, 1440.
87 Second Vatican Ecumenical Council, Pastoral Constitution on the Church in the Modern World Gaudium et Spes, 14.
— Veritatis Splendor 48