Natural moral law is the divine and natural law written on every human heart by God to guide humans toward doing good and avoiding evil (CCC 1954, 1955). Established at creation, this law is universal and immutable, serving as a participation in God’s wisdom and goodness (CCC 1958). It expresses the fundamental dignity of the human person and determines their basic rights and duties (CCC 1956). Because it is rooted in the heart, it cannot be destroyed or removed, and it continues to rise in individuals and societies even when its principles are rejected (CCC 1958).

Human reason enables the discernment of good and evil through the natural law by participating in the wisdom of God (CCC 1954). This capacity is reflected in the human conscience, which allows individuals to distinguish right from wrong (Rom 2:14-15). However, the natural law is not immediately perceived by everyone and requires grace and divine revelation to be known with certainty. This necessity arises because the sinful state of humanity obscures reason and distorts the will, making revelation essential to fully understand the natural law (CCC 2072).

The natural law is one expression of the broader moral law, which also encompasses eternal, revealed, civil, and ecclesiastical laws (CCC 1952). It provides the moral foundation for the structure of moral rules, the building of human community, and the creation of civil law (CCC 1959). The revealed law, specifically the Ten Commandments of the Decalogue, provides a full explanation of the requirements of the natural law (CCC 2071). This entire moral order finds its fullness and unity in Jesus Christ, who is the end of the law and the way of perfection (Rom 10:4, CCC 1953). The New Law of the Gospel further perfects the divine law through the grace of the Holy Spirit and the interior law of charity (CCC 1965-1966).

The natural law also governs human sexuality and marriage. It dictates that the unitive and procreative aspects of the marriage act are inseparable and inherent (CCC 2364-2368). Because of this, homosexual acts are considered intrinsically disordered and contrary to the natural law, rendering them morally unacceptable (CCC 2357). Despite this, individuals with such tendencies must be treated with respect, compassion, and sensitivity to avoid unjust discrimination (CCC 2358).

Regarding social and political order, the moral legitimacy of any authority derives from God’s natural law rather than from the authority itself (CCC 1902). To remain legitimate, authority must act for the common good using morally licit means (CCC 1903). This framework also establishes the right to religious liberty as a natural right of the human person, rooted in their dignity and the freedom to assent to divine truth (CCC 2106).

Finally, the natural law informs economic and environmental stewardship. Any economic system that prioritizes profit or economic factors over human relationships is contrary to human nature (CCC 2423, 2424). Similarly, while humans have dominion over creation, this power is limited by a religious respect for the integrity of creation and a concern for the quality of life of one’s neighbor (CCC 2415). This includes showing kindness to animals, as causing them needless suffering is contrary to respect for the integrity of creation. (CCC 2418).