Have you ever done something that caused an unintended consequence? Unfortunately, that’s life. With everything we do, there are always intended and unintended consequences. As much as we would like to account for every possible outcome and act in a way to limit potential harm, such a goal can never been realized to perfection. No matter what we do, we will always cause something to go wrong.
Should this give us reason for despair? Hopefully not. When approaching this situation from the perspective of moral theology, we know that, even if an act is sinful, it cannot be a “mortal sin” unless we have full knowledge and intent in our action; accidents or results that come because of an alternative intention do not place blame upon us.
The reason for this is often the “principle of double effect,” a concept presented by St. Thomas Aquinas in the 13th century. In essence, it protects someone from the guilt of sin as a result of unintended acts, even if the person knew the effect was going to happen.
Take the classic case of self defense as an example. Someone is attacking you. What do you do? The natural reaction is to preserve one’s life: try to disarm your attacker with your own force or violence. In the process, it’s possible that you will hurt or even kill your attacker, something that can never be heralded as a good. But since your intention was to save your own life and not to take theirs, you are free from moral guilt.
As I explain in this video, there are four criteria that need to be present in order for this principle to apply. It’s very philosophical and may seem like mental gymnastics to justify an action, but we must always remember its intent: to encourage us to will what is good at all times. Bad things cannot be willed to justify good effects, only good ones. We cannot get so caught up in the effects, possible or realized, that we change what we work for or fail to act. In every action, there are intended and unintended consequences. All we can ever worry about is doing what is good.