Saint Thomas Aquinas#
Saint Thomas Aquinas (1225–1274) was an Italian Dominican friar, theologian, and philosopher, widely regarded as one of the most influential thinkers in Western philosophy and Christian theology. He is best known for integrating Aristotelian philosophy with Christian doctrine. His intellectual legacy continues to shape Catholic thought and moral philosophy to this day.
Aquinas’s ethical ideas are primarily developed in two major works:
Summa Theologiae (1265–1274): His most comprehensive and systematic exposition of Christian theology and ethics.
Summa Contra Gentiles (1259–1265): A work intended to explain and defend Christian doctrine, where moral and philosophical arguments are also presented.
Natural law#
Aquinas argues that an act is moral when it accords with the natural law, which he understands as the rational order established by God in the creation of the world and of life itself. Nevertheless, for Aquinas, knowledge of the natural law does not require an explicit acknowledgment of God’s existence; human reason alone is sufficient to discern it.
The natural law comprises these fundamental precepts:
Self-preservation: Every being seeks to preserve its own existence.
Procreation and the upbringing of offspring: Living creatures ensure the continuation of their kind through reproduction and the nurturing of their young.
Rational and social life: Human beings have a natural inclination to seek truth and to live in community with others.
Moral action: Humans are naturally disposed to act in accordance with the natural law, both for their own good and for the good of others.
Aquinas acknowledges Aristotle’s insight that the natural law aims at the flourishing of individuals within a community. Thus, Aristotle’s functional argument is, for Aquinas, a rational one, and it forms an integral part of the natural law itself.
Circumstances and intention#
Aquinas agrees with Aristotle that the circumstances surrounding an action matter, and that practical wisdom must be exercised to determine whether a particular act is moral. He calls this virtue prudence. Nevertheless, Aquinas maintains that the natural law itself is absolute: no set of circumstances can make an act contrary to natural law good. Circumstances may only corrupt a good act. They can, however, mitigate culpability. Aquinas acknowledges that if a person commits an evil act under duress, they may possess some degree of justification, even if the act itself remains immoral.
Likewise, Aquinas concurs with Kant that the intentions behind actions are morally significant, and that the outcomes of actions must be assessed in light of the natural law. A person should therefore reflect on the likely consequences of their actions; if, within the limits of their rational understanding, they believe the outcome to be consistent with natural law, their intention may be deemed good. Yet, while for Kant the only truly good thing is a good will, Aquinas insists that an act contrary to natural law remains wrong regardless of intent. Bad intentions can corrupt a good act, rendering it evil, but good intentions cannot sanctify an act that violates natural law. Nonetheless, intentions may lessen culpability: Aquinas holds that if a person acts out of ignorance, they may possess some justification even if their action is ultimately immoral.
Thus, although Aquinas’s conception of natural law shares common ground with both Aristotle and Kant, it is ultimately more morally stringent. For Aristotle, circumstances and the exercise of practical wisdom are central to moral evaluation. For Kant, intention and rational justification form the core of morality, and only a few moral principles are absolute. For Aquinas, by contrast, adherence to natural law is an essential moral criterion in conjunction with circumstances and intentions.
Intellectual virtues#
Aquinas reinterprets Aristotle’s virtues in light of their capacity to guide human behavior in accordance with the natural law. Among these, he identifies four as fundamental, often referred to as the cardinal virtues:
Prudence (Practical Wisdom): The virtue that directs all the others by guiding us to choose the proper means toward good ends. It enables us to discern what is morally right in specific circumstances, to act according to reason, and to avoid error. Prudence evaluates circumstances and consequences in light of the natural law, harmonizing intellect and will so that we act rightly.
Temperance: The virtue of moderation in the use of created goods. It restrains desires and passions, particularly those related to bodily pleasure, so that appetite remains under the control of reason. Temperance promotes harmony between reason and natural inclination.
Justice: The steadfast will to give each person their due. Justice governs our relationships with others, orienting human action toward fairness, equity, and social order. It safeguards the rights of others and upholds the obligations prescribed by natural law.
Fortitude: The virtue that strengthens the will to face difficulties and endure trials for the sake of the good. It enables perseverance in morally upright action despite fear or adversity, helping maintain integrity and constancy in pursuit of virtue.
Eternal Law#
Aquinas argues that the natural law forms part of the divine will, the eternal law by which creation was designed and ordered. The eternal law itself, however, lies beyond the full grasp of human reason; the intellect alone cannot comprehend it completely. For Aquinas, the eternal law is universal and immutable: it applies to every creature, at all times, and in all places.
In the Christian tradition, the revealed dimensions of the eternal law include the following:
Mysteries of Faith
The Trinity: One God in three Persons (Father, Son, Holy Spirit);
The Incarnation: God becoming man in Jesus Christ;
The Resurrection of Christ.
Specific Divine Commands
Observing the sacraments (e.g., baptism, Eucharist);
The Ten Commandments in their revealed form;
Specific religious rites, prayers, or fasts mandated by God.
Salvation and Supernatural Ends
The path to eternal life in heaven;
The reality of hell and eternal punishment;
The necessity of grace for salvation.
Theological virtues#
The theological virtues are habits of mind and character that perfect the will and elevate the moral life. Though not strictly necessary for moral conduct, they strengthen one’s resolve to act rightly and sustain perseverance in the face of hardship. Unlike the intellectual virtues, however, the theological virtues cannot be attained through reason alone. They require participation in the rituals of the faith community and engagement with the sacred scriptures handed down through tradition. Through such practice, a person may be graced with divine illumination, an insight into the eternal law.
The theological virtues are:
Faith: The virtue by which human beings believe in and accept the truths of the eternal law, even though complete knowledge of these truths is attainable only after death.
Hope: The virtue by which human beings trust in God’s providence and in the ultimate fulfillment of the divine plan, even in the absence of complete certainty in this life.
Love: The virtue by which human beings direct their will toward God for His own sake, without ulterior motive, and extend their love toward others in accordance with the eternal law.
Circle of morality#
Aquinas ethics provide philosophical foundation to Christian traditions. These traditions are rooted in a lineage of belief handed down from ancestors, the conviction that God has revealed His will to a select few, and that this divine will has been recorded in the Holy Scriptures. This belief underpins the conclusion that following natural law is moral, because natural law is an expression of God’s will.
However, Aquinas moves beyond these traditions to search for universal laws. His reasoning bears a strong resemblance to that of Kant: a universal law is immutable and applies to all beings. From these basic principles, and through observation of nature and tradition, Aquinas derives a universal moral law in accordance with nature.
For Aquinas, morality consists in conforming to nature’s rational precepts. Human rationality enables the recognition of fundamental moral values; yet, because rationality itself is part of the natural law, any truths discovered through reason must also be accepted as elements of that law.
Thus, Aquinas’ view aligns with Kant’s concept of the categorical imperative, which serves as a criterion for judging moral and immoral actions. The key difference lies in Aquinas’ treatment of conditional acts. While Kant excludes conditional situations from the scope of moral discourse, since they cannot yield categorical imperatives, Aquinas evaluates such actions in light of the natural law, thereby filling the gap Kant leaves open.
Furthermore, Aquinas would find no conflict with a stricter test of morality, according to which a maxim is moral only if it can be universalised, while its opposite cannot. Very few principles meet this stronger criterion: truthfulness, justice, and respect for life among them. Aquinas would likewise regard each as a precept of the natural law.
Aquinas moral guidelines#
Do good and avoid evil: Help others, speak truthfully, act kindly. Build habits of virtue by consistently doing small good deeds. Contribute to community welfare, through civic duty, service, or ethical work.
Seek virtue: Think before acting; weigh consequences carefully. Treat everyone fairly and give others what is due to them. Persevere in doing good despite fear or hardship. Practice moderation in pleasure, consumption, and emotion. Show charity through kindness, forgiveness, and service.
Reflect on your actions: Use reason and conscience to discern right from wrong. Before acting, ask: What am I doing? Why am I doing it? What are the effects and context? Seek moral advice when intentions are unclear or mixed.
Own your moral choices: Educate your conscience through study, prayer, and moral reflection. Reflect on past decisions and learn from them. When your conscience warns you, stop and reassess your action or motive.
Embrace the eternal law: Seek divine help through prayer and the sacraments. Be humble about personal limits; seek God’s grace to overcome weakness. Strive to unite natural virtues with spiritual virtues.