In order to communicate his goodness and eternal bliss, God wished to create intelligent and free beings (angels and human beings), to whom He freely communicated a participation in his divine nature, which theology calls sanctifying grace. This divine gift, which is received through faith and baptism, and which makes us an adopted child of God, is initially like a seed which is to develop and grow until it reaches its eschatological fullness after death in eternal life. The Christian life is man’s life as a child of God in Christ through the Holy Spirit, which takes place between baptism and the passage to eternal life. The supreme moral rule of Christian life is this divine salvific plan which moral theology calls the eternal law.
The eternal law and the natural moral law
The concept of law is analogous. The eternal law, the natural law, the New Law or Law of Christ, the human political and ecclesiastical laws are moral laws in a very different sense, although they all have something in common.
Eternal law is the plan of divine Wisdom to lead all creation to its end or aim. For the human race, this involves God’s eternal saving plan, by which He has chosen us in Christ “to be holy and blameless before him,” and “destined us in love to be his sons through Jesus Christ.” In this plan is found our full happiness, which consists in the vision of God and, in this world and not yet fully, in the life of union with Christ, who always desires our good.
God leads every creature to its end in accord with its nature. Specifically, “God provides for man differently from the way in which he provides for beings which are not persons. He cares for man not ‘from without,’ through the laws of physical nature, but ‘from within,’ through reason, which, by its natural knowledge of God's eternal law, is consequently able to show man the right direction to take in his free actions.”
The natural moral law is the rational creature’s participation in the eternal law. We cannot directly see God’s eternal design to bring us to full happiness, since we cannot see what is in the mind of God. But by giving us a light that enables us to distinguish what is good and what is evil for us, God enables us to know a part of his eternal plan. That is why we can say that the natural moral law is “itself the eternal law, implanted in beings endowed with reason, and inclining them towards their right action and end.” It is, therefore, a divine (both divine and natural) law. What the natural moral law makes known to us has the force of law insofar as it is the voice and interpreter of the “higher reason” of the divine Lawgiver, in which our spirit participates and to which our freedom is ordered. It is called natural because it consists in the light of reason which every person has by human nature.
The natural moral law is a first step in the communication to mankind of the divine plan of salvation, the full knowledge of which is made possible only by revelation. As has been said, this divine design is that all men and women may attain full happiness in the vision of God.
– Properties. The natural moral law is universal because it extends to every human being, in every epoch. Despite the diversity of cultures throughout history, human intelligence maintains its unity, which makes dialogue between different cultures possible, however difficult this may seem at times.
“The natural law is immutable and permanent throughout the variations of history; it subsists under the flux of ideas and customs and supports their progress. The rules that express it remain substantially valid.” The fundamental principles are immutable, which, when applied to a changing social reality, can give rise to different specific applications, while what is fundamental remains in force.
It is obligatory because, in order to tend towards God, we must freely do good and avoid evil; and hence we must be able to distinguish good from evil, which is possible above all thanks to the light of natural reason. The observance of the natural moral law can sometimes be difficult, but it is never impossible.
– Knowledge of the natural law. The precepts of the natural law can be known by everyone through their reason. Nevertheless, not all its precepts are perceived by everyone in a clear and immediate way. The effective knowledge of these precepts may be conditioned by each one’s personal dispositions, by the social and cultural environment, by the education received, and so on. We could say that natural law is as natural as language: every healthy person has the capacity to speak, but in fact each one will speak more or less correctly and elegantly according to one’s level of education. The natural capacity to know good and evil needs adequate formation in order to effectively attain all the moral truths it can attain.
The divine-positive law
Since in our present situation we suffer from the after-effects of sin, which can obscure our intelligence to a greater or lesser extent, grace and Revelation are necessary so that moral truths can be known by all men and women “without difficulty, with a firm certainty and without mixture of error.” Divine revelation has taken place through a gradual process throughout history.
The Old Law, revealed by God to Moses, “is the first state of the revealed Law. Its moral prescriptions are summed up in the Ten Commandments,” which express immediate conclusions of the natural moral law. The whole economy of the Old Testament is above all ordered to prepare, announce and signify the coming of the Saviour.
The New Law or Gospel Law or Law of Christ “is the grace of the Holy Spirit given through faith in Christ. The external precepts also mentioned in the Gospel dispose one for this grace or produce its effects in one's life.”
The main element of the Law of Christ is the grace of the Holy Spirit, which heals the whole person and is manifested in faith that works through love. It is fundamentally an internal law, which gives the inner strength to do what it teaches. Secondly, it is also a written law, found in our Lord’s teachings (the Discourse on the Mount, the beatitudes, etc.) and in the moral catechesis of the Apostles, which can be summed up in the commandment of love. The grace of the Holy Spirit, infused in the heart of the believer, necessarily entails “living according to the Spirit” and is expressed through the “fruits of the Spirit,” which are opposed to the “works of the flesh”.
The Church, through her Magisterium, is the authentic interpreter of the natural law. This explanation of the natural law is not confined to the faithful alone, but – by Christ’s command: euntes, docete omnes gentes, “go therefore, and teach all nations” – embraces all men and women. Hence the responsibility incumbent on Christians to teach the natural moral law, since by faith and with the help of the Magisterium, they can know it easily and without error.
Civil laws are the norms issued by the government authorities (generally by the legislative body) for the purpose of promulgating, making explicit or concretising the requirements of the natural moral law needed to make possible and adequately regulate the life of citizens in society. These laws must primarily guarantee peace and security, liberty, justice, the protection of the fundamental rights of the person and public morality.
The virtue of justice entails the moral obligation to comply with just civil laws. The gravity of this obligation depends on the greater or lesser importance of the content of the law for the common good of society.
Laws that are opposed to the natural moral law and to the common good of society are unjust. More specifically, laws are unjust:
1) which prohibit doing something that is morally obligatory for citizens or which command them to do something that cannot be done without committing a moral fault;
2) those which positively harm or deprive of due protection goods that belong to the common good: life, justice, fundamental rights of the person, marriage and the family, etc.;
3) those which are not legitimately enacted;
4) those which do not distribute burdens and benefits fairly and proportionately among citizens.
Unjust civil laws do not bind in conscience; on the contrary, there is a moral obligation to refuse to comply with their provisions, especially if they are unjust for the reasons indicated in 1) and 2), and to express one’s disagreement and to try to change them as far as possible or, at least, to reduce their negative effects. Sometimes conscientious objection will have to be resorted to.
Church laws and the commandments of the Church
In order to save us, God also willed that men and women should form a society: the Church, founded by Jesus Christ, and endowed by Him with all the means needed for the fulfilment of her supernatural end, which is the salvation of souls. Among these means is legislative power, which the Roman Pontiff has for the universal Church and the diocesan Bishops – and the authorities equivalent to them – for their own circumscriptions. Most of the laws of universal scope are contained in the Code of Canon Law. There is one Code for the faithful of the Latin rite and another for those of the Eastern rite.
The ecclesiastical laws give rise to a real moral obligation which will be grave or light according to the gravity of the matter.
The most general commandments of the Church are five: 1º to hear Mass in its entirety on Sundays and days of obligation; 2º to confess mortal sins at least once a year, and in danger of death, and if one is to receive Communion; 3º to receive communion at least once a year, at Easter; 4º to fast and abstain from eating meat on the days established by the Church; 5º to help the Church in her needs.
“Conscience is a judgment of reason whereby the human person recognizes the moral quality of a concrete act that he is going to perform, is in the process of performing, or has already completed.” Conscience formulates “moral obligation in the light of the natural law: it is the obligation to do what the individual, through the workings of his conscience, knows to be a good he is called to do here and now.” Thus, for example, when at the end of the day we make an examination of conscience, we may realise that something we said was contrary to charity. Or when we reflect before doing something, our conscience may make us realise that the action we planned would harm a person’s right, and would therefore be a fault against justice.
Conscience is “the proximate norm of personal morality,” so when we act against it we commit a moral wrong. This role of proximate norm belongs to conscience not because it is the supreme norm, but because it has for the individual an unavoidable ultimate character: “the judgment of conscience states ‘in an ultimate way’ whether a certain particular kind of behaviour is in conformity with the law.” When a person judges with certainty, after having examined the problem with all the means at one’s disposal, there is no further appeal to a “conscience of conscience,” or a “judgement of judgement,” because otherwise one would proceedad infinitum.
A right or true conscience is one which judges the moral quality of an act with truth, and an erroneous conscience is one which does not attain the truth, and regards as good an action which in reality is evil, or vice versa. The cause of an error of conscience is ignorance, which can be invincible (and inculpable), if it dominates the person to such an extent that there is no possibility of recognising and overcoming it; but this ignorance is culpable or guilty if it could be recognised and overcome, but the person does not want to use the means needed to overcome it. A guilty erroneous conscience does not excuse from sin, and can even aggravate it.
Conscience is certain when it makes a judgement with the moral certainty that it is not mistaken. It is said to be probable when it judges with the conviction that there is a certain probability of error, but that this is less than the probability of being right. It is said to be doubtful when the probability of being wrong is assumed to be equal to or greater than the probability of being right. Finally, it is called perplexed when it does not dare to judge, because it thinks that it is a sin both to perform an act and to omit it.
In practice, one should follow only a conscience that is certain and true, or a conscience that is certain and invincibly wrong. One should not act with a doubtful conscience, but should try to get out of doubt by praying, studying, asking questions, etc.
The formation of conscience
Morally wrong actions carried out in invincible ignorance are harmful to the one who commits them and perhaps also to others, and in any case they can contribute to a further darkening of conscience. Hence the imperative need to form one’s conscience.
To form an upright conscience, it is necessary to instruct the intellect in the knowledge of the truth – for which one can count on the help of the Church’s Magisterium – and to educate the will and emotions through the practice of the virtues. This is a task that lasts a lifetime.
In forming one’s conscience, humility, which is acquired by being sincere before God, and spiritual direction are particularly important.
A well-formed conscience needs to practise the moral virtue of epikeia. Epikeia leads to acting differently from the letter of the law when, faced with a situation not foreseen by the general formulation of the law, acting in accord with the law would be wrong or harmful. Thus, for example, police authorities may stipulate that one can only enter and leave the international area of an airport through the gates intended for that purpose. This refers to ordinary behaviour. But it is clear that in the event of an earthquake that destroys the entrances and prevents the use of those gates, the people inside must escape in whatever way they can. The authority’s provisions, expressed in general terms, refer to ordinary behaviour, and not to exceptional circumstances that no one foresaw.
Catechism of the Catholic Church, 1730-1742, 1776-1794 and 1950-1974.
Saint John Paul II, Encyclical Veritatis splendor, 6 August 1993, 28-64.
Saint Josemaría, Homily “Freedom, A Gift from God,” in Friends of God, 23-38.
 Cf. Saint Thomas Aquinas, S.Th, I-II, q. 93, a. 1, c.; Second Vatican Council, Dignitatis humanae, 3.
 Eph 1:4-5.
 Saint John Paul II, Veritatis splendor, 6 August 1993, 43.
 Cf. Ibid.; Saint Thomas Aquinas, S.Th, I-II, q. 91, a. 2.
 Cf. Saint John Paul II, Veritatis splendor, 44.
 Cf. Ibid.
 Cf. Catechism, 1956.
 Ibid., 1958.
 “The application of the natural law varies greatly; it can require a reflection adapted to the multiplicity of conditions of life according to places, times and circumstances. Nevertheless, in the diversity of cultures, the natural law remains a norm which binds people together and imposes on them, over and above the inevitable differences, common principles” (Catechism, 1957).
 Cf. Saint John Paul II, Veritatis splendor, 42.
 Cf. Ibid., 102.
 Cf. Catechism, 1960.
 Pius XII, Humani generis: DZ 3876. Cf. Catechism, 1960.
 Catechism, 1962.
 Cf. Second Vatican Council, Dei verbum, 15.
 Saint John Paul II, Veritatis splendor, 24. Cf. Saint Thomas Aquinas, S.Th, I-II, q. 106, a. 1, c. and ad 2.
 Cf. Saint Thomas Aquinas, S.Th, I-II, q. 108, a. 1.
 Cf. Gal 5:16-26.
 Cf. Catechism, 2036.
 Mt 28:19.
 Cf. Saint Thomas Aquinas, S.Th, I-II, q. 95, a. 2; Catechism, 1959.
 Cf. Saint John Paul II, Evangelium vitae, 25 March 1995, 71.
 Cf. Catechism, 2242-2243; Saint John Paul II, Evangelium vitae, 72-74.
 Cf. Second Vatican Council, Lumen gentium, 9.
 Cf. Council of Trent, Canons on the Sacrament of Baptism, 8: DZ 1621.
 Cf. Catechism, 2042.
 Cf. Ibid.
 Cf. Ibid.
 Cf. Ibid., 2043.
 Cf. Ibid.
 Catechism, 1778.
 Saint John Paul II, Veritatis splendor, 59.
 Ibid., 60.
 Cf. Ibid.
 Ibid., 59.
 Cf. Ibid., 62; Second Vatican Council, Gaudium et spes, 16.
 A certain, invincibly erroneous conscience is a moral rule, but not in an absolute way: it is binding only for as long as the error remains. And it does so not because of what it is in itself: the binding power of conscience derives from truth, so that an erroneous conscience can bind only to the extent that it is subjectively and invincibly considered to be true. In very important matters (deliberate homicide, etc.), it is very difficult to have an inculpable error of conscience.
 Cf. Catechism, 1783.
 Cf. Saint John Paul II, Veritatis splendor, 64.
 Cf. Catechism, 1784.