The Doctrine of Double Effect

The problem of the trolley is based on a principle known as the doctrine of double effect. This principle, first introduced by Thomas Aquinas, is the notion that an action can be morally permissible even when one of the consequences is morally bad. The bad consequence of these actions is foreseen, like in the problem of the trolley, where you realize ahead of time that one man will die if the lever is pulled.

So if harming others is considered immoral, and we can foresee that one of the consequences involves harming another person, is the person who pulls the lever morally wrong?

According to the doctrine of double effect, an individual can morally perform an action that leads to foreseen harmful consequences if the following four conditions are met:

  1. There must be intention for the good consequence. The good consequence should never be used as an excuse for the bad consequence, so there should never be the intention to have the bad consequence occur.
  2. The action itself must be morally neutral or good, and never morally wrong. So if you were to isolate the action from the good and bad consequences, it should never be bad.
  3. The good consequence must be the direct result of the action, and not the result of the bad consequence. A morally good consequence can never occur because the action initially created a bad consequence.
  4. The bad consequence can never outweigh the good consequence. Even if the intent was good, if the result leads to the bad consequence overpowering the good consequence, then this condition has been violated.

A common real-life example of the doctrine of double effect is when someone is killed out of self-defense. If someone kills his attacker, the action is morally permissible because the good consequence outweighs the foreseen bad consequence (killing another person).

The doctrine of double effect is rejected by consequentialists because according to consequentialism, there is no relevance to what a person intended; only the consequences of his actions matter.

To this day, the questions of morality proposed by the trolley problem continue to spark debate in the philosophical world.