1. The freedom of God’s children
Human freedom has various dimensions. Freedom from coercion is the freedom to carry out externally what one has decided upon, without impediments from outside agents. Examples of this are freedom of expression, freedom of organization, etc. Freedom of choice or psychological freedom connotes the absence of the internal need to choose one thing or another. This refers not to the freedom to do something , but rather to decide autonomously , without being bound by an interior determinism. In the moral sense , freedom refers to the capacity to affirm and love the good, which is the object of one’s free will, without being enslaved by disordered passions or by sin.
God wanted human freedom so that man “might of his own accord seek his Creator and freely attain his full and blessed perfection by cleaving to him. Man’s dignity requires him to act out of conscious and free choice, as moved and drawn in a personal way from within, and not by blind impulses in himself or by mere external constraint. Man gains such dignity when, ridding himself of all slavery to the passions, he presses forward towards his goal by freely choosing what is good, and, by his diligence and skill, effectively secures for himself the means suited to this end.” 
Freedom from external coercion, from internal necessity and from disordered passions, in a word, full human freedom possesses a great value because only thus can we love (freely affirm) the good because it is good, and as a result love God as the Greatest Good; by doing so we imitate divine Love and attain the end for which we were created. Thus we can say that “authentic freedom is an exceptional sign of the image of God in man.” 
Sacred Scripture considers human freedom in the light of salvation history. On account of the original fall, the freedom man had received from God became subject to the slavery of sin, although it was not completely lost (cf. Catechism , 1739-1740). By his glorious Cross, announced and prepared for in the Old Testament, “Christ has won salvation for all men. He redeemed them from the sin that held them in bondage” ( Catechism , 1741). Only by cooperating with the grace that God gives through Christ can man enjoy complete freedom in the moral sense: for freedom Christ has set us free (Gal 5:1; cf. Catechism , 1742).
The possibility that man might sin did not stop God from deciding to create us free. Human authorities should respect freedom and not place limits beyond those required by just laws. But at the same time one shouldn’t forget that for decisions to be good it is not enough that they be free, and that only in the light of the immense value of freely affirming the good can one understand the ethical requirement to respect people’s fallible freedom.
2. Natural moral law
The concept of law is analogous. The natural law, the New Law or the Law of Christ, and human laws, both political and ecclesiastical, are all moral laws in distinct senses, although all have something in common.
Eternal law refers to the plan of divine Wisdom leading all creation towards its goal.  In mankind’s regard, it corresponds to God’s eternal salvific plan, by which he chose us in Christ before the foundation of the world, that we should be holy and blameless before him . . . to be his sons through Jesus Christ ( Eph 1:4-5).
God guides every creature towards its end according to its nature. “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.” 
Natural moral law is the participation in the eternal law by the rational creature.  The natural 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 law (divine-natural). It consists of the very light of reason that enables man to discern good from evil, and has the force of law as the voice and interpreter of the “higher reason” of the divine Lawgiver, in which our spirit participates and to which our freedom adheres.  It is called “natural” because it consists of the light of reason that each person has by nature.
Natural moral law is a first step in the communication to all humankind of the divine salvific plan, whose complete unveiling is only made possible by Revelation. The natural law “hinges upon the desire for God and submission to him, who is the source and judge of all that is good, as well as upon the sense that the other is one’s equal” ( Catechism , 1955).
— Properties . The natural law is universal because it encompasses every human person, of every epoch (cf. Catechism , 1956). “It 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” ( Catechism , 1958).  It is obligatory because, in order to reach God, man must freely do good and avoid evil. Thus he needs to be able to distinguish good from evil, which happens above all thanks to the light of natural reason.  The observance of the natural moral law can sometimes be hard, but it is never impossible. 
— Knowledge of the natural law . The precepts of the natural law can be known by all men and women through their reason. Nonetheless, in fact not all its precepts are perceived by everyone in an immediate and clear way (cf. Catechism , 1960). Its effective knowledge can be conditioned by personal dispositions, by the social and cultural climate, by one’s education and upbringing, etc. Since mankind’s present situation is still subject to the effects of sin, grace and Revelation are necessary for moral truths to be known “by everyone with facility, with firm certainty and with no admixture of error.” 
3. Divine-positive law
The Old Law, revealed by God to Moses, “is the first stage of revealed Law. Its moral prescriptions are summed up in the Ten Commandments” ( Catechism , 1962), which expresses immediate conclusions of the natural moral law. The entire economy of the Old Testament is ordered above all to preparing, announcing, and signifying the coming of the Savior. 
The New Law or the 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 principal element of the Law of Christ is the grace of the Holy Spirit, which heals the whole person and is expressed in a faith that works through love.  It is above all an internal law, which gives the interior strength needed to achieve what it teaches. In second place, it is also a written law that is found in Christ’s teachings (in the Sermon on the Mount, the Beatitudes, etc.) and in the moral catechesis of the apostles, and which can be summed up in the commandment of love. This second element is not of secondary importance. The grace of the Holy Spirit, infused in the believer’s heart, necessarily implies “living according to the Spirit” and is expressed via the “fruits of the Spirit,” which are opposed by the “works of the flesh” (cf. Gal 5:16-26).
The Church, through its Magisterium, is the authentic interpreter of the natural law (cf. Catechism , 2036). This mission is not restricted only to the faithful, but—by Christ’s command: euntes, docete omnes gentes ( Mt 28:19)—encompasses all men and women. Hence the responsibility of all Catholics to teach the natural moral law, since by faith and with the assistance of the Magisterium they can know it easily and without error.
4. Civil laws
Civil laws are the normative dispositions decreed by state authorities (generally, by the legislative branch of the state) with the purpose of promulgating and making explicit the demands of the natural moral law needed to make possible and regulate adequately the life of its citizens in the sphere of a politically organized society.  These laws should principally guaranty peace and security, freedom, justice, the safeguarding of fundamental rights of the person and public morality. 
The virtue of justice entails the moral obligation to obey 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.
Unjust laws are those that oppose the natural moral law and the common good of society. More specifically, unjust laws are those:
1) that prohibit citizens from doing something they are morally obligated to do, or that order them to do something they cannot do without committing a moral offense;
2) that harm or deprive of due safeguards goods pertaining to the common good: life, justice, fundamental rights of the person, marriage and the family, etc.;
3) that are not legitimately promulgated;
4) that fail to distribute burdens and benefits in an equitable and proportioned way among the citizens.
Unjust civil laws do not oblige in conscience; to the contrary, there is a moral obligation not to obey them, above all if they are unjust for the reasons indicated in 1) and 2), to make clear one’s disagreement with them, and to try to change them insofar as possible or, at least, to reduce their negative effects. At times, one may need to appeal to conscientious objection (cf. Catechism , 2242-2243). 
5. Ecclesiastical laws and the precepts of the Church
To save mankind God has also wanted a specific society  : the Church, founded by Jesus Christ and endowed with all the means for fulfilling its supernatural end, which is the salvation of souls. Among these means is legislative authority, held by the Roman Pontiff for the universal Church and by diocesan bishops (and authorities likened to them) for the people they are responsible for. The majority of the laws of universal scope are contained in the Code of Canon Law. There exists a Code for the faithful of the Latin Rite and another for those of the Eastern Rite.
The ecclesiastical laws give rise to an authentic moral obligation  that will be more or less grave according to the gravity of the matter.
The most general precepts of the Church are the following five: first, to attend the entire Mass on Sundays and Holy Days of Obligation (cf. Catechism , 2042); second, to confess one’s mortal sins at least once a year, when in danger of death, and when needed in order to receive communion (cf. Catechism , 2042); third, to receive communion at least once a year, during the Easter season (cf. Catechism , 2042); fourth, to fast and abstain from eating meat on days established by the Church (cf. Catechism , 2043); fifth, to assist the Church in its needs (cf. Catechism , 2043).
6. Freedom and law
Some discussions of moral questions seem to imply that the ethical demands contained in the moral law are external to freedom. Freedom and law seem, then, to be realities that are opposed to one another and that limit each other reciprocally: as though freedom begins where the law ends and vice versa.
The truth is that free behavior does not stem from instinct or from a physical or biological necessity. Instead, it is guided by each person according to each one’s knowledge of good and evil: one freely carries out the good contained in the moral law and freely avoids the evil known by means of the same law.
The denial of the good known through the moral law is not freedom, but sin. What goes against the moral law is sin, not freedom. The moral law clearly requires us to correct any desire to carry out sinful actions: the desire for vengeance, for violence, for stealing, etc. But this moral guidance is not opposed to freedom, which is always directed to the free affirmation of the good, nor is it a coercion of freedom, which always holds out the sad possibility of sinning. “When we breathe this air of freedom we see clearly that evil is an enslavement, not a liberation . . . Such a person may show that he has acted according to his preferences, but he does not speak with the voice of true freedom, because he has become the slave of his decision and he has decided for the worst, for the absence of God, where there is no freedom to be found.” 
A different matter altogether are human laws and rules. Owing to the generality and conciseness of the terms in which these laws are expressed, in a specific case they may not be a true indicator of what a specific person should do. A well formed person knows that in these concrete cases one should do what one knows with certainty to be right.  But there exists no case in which it would be good to carry out the intrinsically evil actions prohibited by the negative precepts of the natural moral law or divine-positive law (adultery, deliberate homicide, etc.). 
7. Moral conscience
“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” ( Catechism , 1778). Conscience specifies our “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 .” 
Conscience is “the proximate norm of personal morality.”  Therefore a person who acts against it commits a moral evil. This function of proximate norm pertains to conscience not because it is the highest norm,  but because it has for the person an ultimate and inescapable nature: “The judgment of conscience states ‘in an ultimate way’ whether a certain particular kind of behavior is in conformity with the law”  : when a person judges with certainty, after having evaluated the problem using all the means at one’s disposal, no ulterior appeal exists—a “conscience of conscience,” a “judgment of judgment,”—because otherwise the process would go on to infinitely.
A right or true conscience refers to a conscience that judges truthfully regarding the moral quality of an act. An erroneous conscience fails to reach the truth, viewing as good an action that in reality is bad, or vice versa. The cause of an erroneous conscience is ignorance , which can be invincible (and blameless) if it dominates a person to such an extent that there is no possibility of recognizing it and amending it; this ignorance may also be vincible (or culpable) if a person can recognize and overcome it but fails to do so because he or she does not want to use the means available.  A culpably erroneous conscience does not excuse from sin, and can actually aggravate it.
Conscience is certain , when it expresses a judgment with the moral certainty of not being mistaken. It is probable when it judges with the conviction that there is some probability of error, but less than the probability of being correct. It is called doubtful when the probability of being mistaken is considered to be equal to or greater than that of being correct. Finally, it is called perplexed when one does not dare to judge because one thinks that both doing an act or omitting it is a sin.
In practice one should only follow a certain and true conscience or a certain invincibly erroneous conscience .  One should not act with a doubtful conscience, but rather first seek to resolve the doubt through prayer, study, asking for advice, etc.
8. Forming one’s conscience
Actions that are morally negative and done with invincible ignorance harm the person who commits them as well as possibly also others. Moreover, they can contribute to a greater darkening of conscience in society as a whole. Hence the urgent need to form one’s conscience correctly (cf. Catechism , 1738).
To form a right conscience requires instructing the intellect in the knowledge of the truth (for which a Catholic relies on the help of the Church’s Magisterium), and educating the will and the emotions through the practice of the virtues.  This is an effort that lasts one’s entire life (cf. Catechism , 1784).
In order to form one’s conscience correctly, humility is especially important, attained by being sincere with God, and in spiritual direction. 
Ángel Rodríguez Luño
Catechism of the Catholic Church , 1730-1742, 1776-1794 and 1950-1974.
John Paul II, Encyclical Veritatis splendor , August 6, 1993, 28-64.
Saint Josemaría, Homily, “Freedom, a Gift from God,” in Friends of God , 23-38.
J. Ratzinger, Conscience and Truth : Presented at the 10th Workshop for Bishops, February 1991, Dallas Texas.
 Second Vatican Council, Gaudium et spes , 17. Cf. Catechism , 1731.
 Ibid .
 Cf. St. Thomas Aquinas, Summa Theologiae , I-II, q. 93, a.1, c; Second Vatican Council, Dignitatis humanae , 3.
 John Paul II, Enc. Veritatis splendor , August, 6, 1993, 43
 Cf. Ibid .; St. Thomas Aquinas, Summa Theologiae , I-II, q.91, a. 2.
 John Paul II, Enc Veritatis splendor , 44.
 Cf. Ibid .
 “Application of the natural law varies greatly; it can demand reflection that takes account of various conditions of life according to places, times, and circumstances. Nevertheless, in the diversity of cultures, the natural law remains as a rule that binds men among themselves and imposes on them, beyond the inevitable differences, common principles” ( Catechism , 1957).
 Cf. John Paul II, Enc. Veritatis splendor , 42.
 Cf. Ibid ., 102.
 Pius XII, Enc. Humani generis : DZ 3876. Cf. Catechism , 1960.
 Cf. Second Vatican Council, Const. Dei verbum , 15.
 John Paul II, Enc. Veritatis splendor , 24. Cf. St. Thomas Aquinas, Summa Theologiae , I-II, q.106, a.1, c. and ad 2.
 Cf. St. Thomas Aquinas, Summa Theologiae , I-II, q. 108, a.1.
 Cf. St Thomas Aquinas, Summa Theologiae , I-II, q. 95, a. 2; Catechism , 1959.
 Cf. John Paul II, Enc. Evangelium vitae , May 25, 1995, 71.
 Cf. John Paul II, Enc. Evangelium vitae , 72-74.
 Cf. Second Vatican Council, Cost. Lumen gentium , 9.
 Cf. Council of Trent, Canons on the Sacrament of Baptism , 8: DZ 1621.
 Saint Josemaría, Friends of God , 37.
 Cf. St. Thomas Aquinas, Summa Theologiae , I-II, q. 96, a. 6 and II-II, q. 120.
 Cf. John Paul II, Enc. Veritatis splendor , 76, 80, 81, 82.
 John Paul II, Enc. Veritatis splendor , 59.
 Ibid ., 60.
 Cf. Ibid ., 60.
 Ibid ., 59.
 Cf. Ibid ., 62; Second Vatican Council, Gaudium et spes , 16.
 A certain invincibly erroneous conscience is not a moral rule in an absolute way: it obliges only while it remains in error. And it does so not on account of what it is in itself: the obligatory force of conscience derives from the truth, and therefore an erroneous conscience can oblige only to the extent that subjectively and invincibly it is considered truthful. In very important matters (deliberate homicide, etc.) it is difficult to have an erroneous conscience that is inculpable.
 Cf. John Pau II, Enc. Veritatis splendor , 64
 “Spiritual guidance should not be used to turn people into beings with no judgment of their own, who limit themselves to carrying out mechanically what others tell them. On the contrary, it should tend to develop men with their own Christian standards. This requires maturity, firm convictions, sufficient doctrinal knowledge, a refined spirit and an educated will” (Saint Josemaría, Conversations , 93).