The Fifth Commandment: “You Shall Not Kill”

Willfully Injuring Or Trying to Hurt Another Person

It is not exactly the most obvious of mortal sins against this commandment, after all, why is hurting somebody a mortal sin when you don’t kill them?

When you are willfully trying to injure or hurt another person, generally speaking there is hatred in your heart. Remember that hatred is a mortal sin. You then take that hatred and give it a physical manifestation, that is hurting another person or injuring them.

The thing is, when we strike at another individual with this intention, it is not out of love. We are destroying their body. We break their bones, or tear their skin. We draw forth blood, blood that should remain within their bodies.

We are killing parts of their bodies. They may still be alive, but we are killing body parts.

St. Paul writes in the first letter to the Corinthians:

Or know you not, that your members are the temple of the Holy Ghost, who is in you, whom you have from God; and you are not your own? For you are bought with a great price. Glorify and bear God in your body. 1 Corinthians 6:19-20

Each and every single person, Catholic or Protestant, Muslim or Jew, Pagan or Atheist, has a body, and that body is a temple for the Holy Spirit. They also have the free will to choose to become Catholic to embrace salvation. But regardless, the body is meant as a dwelling place for the Holy Spirit to reside. Attacking another person (especially a Catholic) is desecration of the body. Physically harming a priest, bishop, cardinal or pope gives an automatic excommunication.

What about if you are being physically harmed by an assailant? Are you allowed to defend yourself by causing physical harm to them?

Yes. We must look at St. Thomas Aquinas’ principle of double effect. Double effect is comprised of 3 principles being (taken from Wikipedia):

1. The nature of the act is itself good, or at least morally neutral;
2. The agent intends the good effect and not the bad either as a means to the good or as an end itself;
3. The good effect outweighs the bad effect in circumstances sufficiently grave to justify causing the bad effect and the agent exercises due diligence to minimize the harm.
   

When it comes to self-defense and using the principle of double effect we find that it is okay because:

1. The act of defending one’s self from physical harm is a good. We have every right to live.
2. You are intending to defend yourself from the assailant. You are hurting them, but that is not your intention. You are not seeking out their injury.
3. You are defending yourself and are using your best means to subdue the individual with the minimal damage to them as possible. That is if you have to break their arm in order to prevent further harm to come to you, then that is all you do, nothing more. Each situation is different and maybe pinning them is all you need in one circumstance. But, you are using due diligence to determine and assess your situation.

Defending one’s self is not a mortal sin. But causing physical harm is. Boxing and other forms of martial arts, for the purpose of fighting, seems to be a mortal sin as your intention is to hurt each other and cause physical harm. Taking a self-defense class and practicing on each other would fall under double-effect as you are learning so that you can defend yourself if the situation was needed down the road.

Now, St. John Chrysostom is famous for saying in regards to blasphemy:

And should you hear any one in the public thoroughfare, or in the midst of the forum, blaspheming God; go up to him and rebuke him; and should it be necessary to inflict blows, spare not to do so. Smite him on the face; strike his mouth; sanctify your hand with the blow, and if any should accuse you, and drag you to the place of justice, follow them thither; and when the judge on the bench calls you to account, say boldly that the man blasphemed the King of angels!

Notice that St. John actually encourages you to physically harm someone if they commit blasphemy. These would not be sinful to do, as someone who blasphemies against God causes insult to Him. As the blasphemer is causing insult to God, they are causing damage to themselves, and you are defending the Lord.

Intentionally injuring another person or attempting to is a mortal sin. Go to confession.