I’ve written several long posts on the topic of lying, with several more planned. Numerous commentators have also written on this topic, some repeatedly. Why is lying such an important moral issue? In all probability, most actual lies that people tell are venial sins (although lying can be a mortal sin). Why emphasize this subject when the controversy tends to revolve around examples of only venial sin?
The answer is that the discussion about lying is a way of discussing basic questions of morality and the answers given to those questions by the Magisterium, especially the often-disputed often-ignored teaching that certain kinds of acts are intrinsically evil and therefore always immoral. We could consider the same question of intrinsic evil with a discussion of gravely immoral acts, such as abortion and contraception. And in fact there has been much controversy lately about the morality of those acts for the same reason, basic questions of morality are at stake. But lying makes a particularly good basis for the discussion, precisely because many lies are venial sins.
Suppose that a lie is a very grave mortal sin, such as lying under oath during a murder trial with the intention and reasonably anticipated consequence that your lie will cause an innocent person to be convicted and given life in prison (or the death penalty). Should you commit this very grave lie, if you are under some type of duress, if lying will help you avoid dire consequences for yourself? Most Catholics would answer ‘No.’ But some would be answering based on proportionalism, that the gravity of the nature of the act outweighs the gravity of the consequences. Some would answer based on moral relativism, that the act seems immoral to them, therefore it is immoral. Some would answer based on democracy, that the act seems immoral to most persons, therefore it is immoral. And only a few would answer that the act is immoral because lying is intrinsically evil. So the example of a very grave lie does not suffice to reveal the basis for the moral analysis.
But when a lie is a venial sin in the face of dire circumstances, an answer based on proportionality, or relativism, or the majority opinion, etc. will give a different answer than one based on the magisterial teaching about intrinsically evil acts. So a discussion of venial sin is particularly useful to discern correct doctrine on morality and intrinsic evil.
But the questions would be the same:
What must I do? How do I distinguish good from evil?
Do the commandments of God really have the capacity to clarify the daily decisions of individuals and entire societies? Is it possible to obey God and thus love God and neighbor, without respecting these commandments in all circumstances?
What is good and what is sin? How do we determine, in accordance with the truth about the good, the specific rights and duties of the human person?
On what does the moral assessment of man’s free acts depend? What is it that ensures this ordering of human acts to God? Is it the intention of the acting subject, the circumstances — and in particular the consequences — of his action, or the object itself of his act?
How can obedience to universal and unchanging moral norms respect the uniqueness and individuality of the person, and not represent a threat to his freedom and dignity? 
The answers to these questions fall into two categories:
1. the minority position: that every intrinsically evil acts always immoral, solely due to the nature of the act, as determined by its moral object. This position is succinctly described by its chief proponent as follows:
No circumstance, no purpose, no law whatsoever can ever make licit an act which is intrinsically illicit, since it is contrary to the Law of God which is written in every human heart, knowable by reason itself, and proclaimed by the Church. 
The negative precepts of the natural law are universally valid. They oblige each and every individual, always and in every circumstance. It is a matter of prohibitions which forbid a given action semper et pro semper, without exception, because the choice of this kind of behavior is in no case compatible with the goodness of the will of the acting person, with his vocation to life with God and to communion with his neighbor. It is prohibited — to everyone and in every case — to violate these precepts. They oblige everyone, regardless of the cost, never to offend in anyone, beginning with oneself, the personal dignity common to all. 
2. the majority position, in three forms:
a. No act is intrinsically evil or always immoral.
b. Every intrinsically evil act is always immoral, but a good intention or dire circumstances or other considerations can make an act justifiable and no longer intrinsically evil.
c. We should base our ethical decisions on new criteria, so that questions of intrinsic evil and the moral object are unnecessary and never considered.
The majority position is held by most Catholic moral theologians, most online commentators, most of the laity, and perhaps by most priests and religious.
The minority position is actually a dogma of the Roman Catholic Church, taught infallibly by Sacred Tradition and Sacred Scripture and the Universal Magisterium. Whoever knowingly chooses to reject this teaching, commits the sin of heresy.
Ronald L. Conte Jr.
Roman Catholic theologian and Bible translator
 EV 62
 VS 52