What makes a sin “grave”?

Most people know the difference between a mortal and a venial sin. But what constitutes a sin of “grave matter”?




Mortal sin refers to a grave sin which ruptures our friendship with God. The loss of sanctifying grace results from this choice against God and His law. Venial or lesser sin weakens charity and impedes growth in the spiritual life. It does not, however, result in the loss of the charity that God gives us, the basis for friendship with God.


Like so many school children before them, this year’s first penitents will learn that mortal sin consists in knowingly and deliberately committing a sin of grave matter. But how do we know if a sin is grave?


A grave sin is defined by its object—what sort of act one has chosen. The kind of act involved in grave sin is one whereby the sinner, by the very nature of the act, turns against God. This turning can be direct, as in the case of idolatry or apostasy, or it can result from some act of disobedience to God’s commands. The refusal to worship God on Sunday, for example, constitutes a grave turning against His commandments.


Pope John Paul II reminded the Church of the real harm that grave sin introduces into life, as an act which not only gravely offends God, but “ends in turning against man himself” (Reconciliatio et paenitentia, no. 17).

This teaching helps us to appreciate the grave nature of certain acts in and of themselves. Even if committed without full knowledge or a full act of the will, a grave sin remains an obstacle to man’s flourishing and a rupture in the human community.


The Code of Canon Law reminds Catholics that one who has committed a grave sin should refrain from receiving Holy Communion (CIC 916). Catholics are obliged to confess all grave sins not yet brought to the confessional (CIC 988 § 1). All that is to say, grave sin is serious business.


People often ask if a list exists of all sins of grave matter. Given the varieties of human action, such a list is impossible to draw up. In the absence of such a list, however, the Ten Commandments remain the best available guide. As the commandments themselves reveal, some areas of life admit more easily of there being greater and lesser sins. The seventh commandment forbidding stealing, for example, admits of both grave and light matter. Pilfering a day’s wage ruptures the human community in a way that stealing a candy bar does not. The eighth commandment prohibits both vicious lies—sins of grave matter—and so-called white-lies, sins of light matter but nonetheless contrary to human dignity.


Conjugal love occupies an important place in Catholic teaching. It stands out among the goods that God has made for us to enjoy. Unlike money, which one can have in greater or lesser amounts, conjugal love cannot be divided. It is all or nothing. The choice for sexual pleasure involves either the marital embrace or an act of unchastity. Accordingly, no sin against the sixth commandment can be considered a light affair. The ninth commandment forbidding impure thoughts, on the other hand, may admit of light matter.


Taking the life of an innocent person would indisputably be grave matter. Other sins against the fifth commandment could also be considered grave under certain circumstances. Ruining another’s reputation with slander or gossip could so drastically affect one’s livelihood that this sin should by no means be taken lightly.


Sin does not represent the violation of an arbitrary whim, like the rules of a board game. Instead, sin contradicts the truth about the human person. The moral law is like the law of gravity—it is built into human nature. In just the same way, a sin of grave matter means a serious one, serious in its object. The gravity of sins is not arbitrarily assigned. A sin against human life or human love, a choice against God and His Church constitutes a serious wound to man’s capacity for true happiness.



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