Mortal and Venial Sin

Thomas Aquinas desired to explain how the Catholic Church's doctrine that there are mortal and venial sins could be reconciled with the Biblical verse James 2:10, "For whoever keeps the whole law, and yet stumbles in one point, he has become guilty of all". The Catholic Church teaches that there are two levels of sin, mortal sin and venial sin: a mortal sin is a sin that severs us from God's sanctifying grace, and will damn us without repentence; and a venial sin is a sin that does not sever us from God's sanctifying grace, but can lead us to mortal sin. However, this line from James claims that there are no distinctions in sins, and any sin is a violation of the whole law. This would appear to be a contradiction. Using careful distinctions, Thomas Aquinas will argue that, understood rightly, the Church's doctrine teaches that there is only one sort of sin and all sin is of equal weight.

First, he will establish the equal gravity of all mortal sins. The first distinction to be made is the difference between the gravity of the matter of a sin and the gravity of a sin. The matter of a sin is the action done. It is called the "matter" of the sin, since it is what the sin is made of, just like a wall is made of brick. So, for instance, the matter of the sin of murder is killing someone. The matter of sins comes in various degrees of severity. Killing is worse than theft, the killing of a father is worse than killing of a stranger, and beating someone with a baseball bat is worse than slapping him. This, however, is only the gravity of the matter of the sin, not the gravity of the sin itself. All mortal sins are of equal gravity, as the gravity of sins is measured by how much they separate us from God. Since there can be no worse separation than to be separated from God's sanctifying grace and to be eternally damned, all mortal sins are of equal gravity, even if their matter is not.

Second, he will establish the equality of all sins by doing something that might seem surprising. He argues that venial sins are not, strictly speaking, sins. To understand this, one must take a look at Aristotle's Prior Analytics. Aristotle discusses synonymy of language, homonymy of language and, lost to most modern linguistic analysis, paronymy of language. Paronymy is a meaning of a word that is dependant on another, more precise, use of a word. Aquinas's example is the phrase "the urine is healthy". The urine itself isn't synonymously healthy, since it is the person that has health, nor is it homonymously healthy, since to call urine "healthy" is not to have a completely unrelated meaning of "health". Instead the meaning of "healthy urine" is dependent on the meaning of "healthy person" and urine is paronymously "healthy". So too, he argues, are venial sins called "sins". They are paronymously called "sins", since they can lead us to mortal sins, the only sins that are, strictly speaking, sins. However, they are not, strictly speaking, sins themselves, since venial sins do not themselves separate us from God. It is not false to say that venial sins are sins, any more than it is false to say urine is healthy, but, strictly speaking, only mortal sins are sins.

In this way, Thomas Aquinas reconciles the doctrine of mortal and venial sin with James 2:10. His distinctions are useful. His first distinction enables us to continue to coherently rank the severity of actions without needing to rank the severity of sins, and his second distinction makes clear some of the various ways in which terms such as "sin" can be used.