The problem can be rewritten as:
- Is it morally permissible to do an evil act to prevent another evil act?
- Are multiple lives more valuable than a single life?
For the first, it is not permissible to commit a sin. For the second, one could discuss the gravity of that, and one would generally conclude that multiple lives would be more grave than one, but this on its own is of limited use, because the problem is designed to provoke more than this judgement.
Removing the trolley and giving a firearm and saying "
if you don't kill this one person, I'll kill those five people" makes this easy: it is not permissible to kill in this circumstance. In fact, it is not permissible to do any evil.
The sin is within the person:
5 Q. What is actual sin?
A. Actual sin is that which man, after coming to the use of reason, commits of his own free will.
6 Q. How many kinds of actual sin are there?
A. There are two kinds of actual sin: mortal and venial.
7 Q. What is mortal sin?
A. Mortal sin is a transgression of the divine Law by which we seriously fail in our duties towards God, towards our neighbour, or towards ourselves.
10 Q. Besides grave matter, what is required to constitute a mortal sin?
A. To constitute a mortal sin, besides grave matter there is also required full consciousness of the gravity of the matter, along with the deliberate will to commit the sin.
The use of death as the example is intended to cloud judgement by making it a matter of emotion, but the
worst sins are the most dangerous and often difficult to appreciate.
There are treatments of
double effect and
mental reservations which can be significant in some circumstances, but in general, morality is far more straightforward.
Redirecting the trolley is thus evil if done to kill another, but good if intended to save others. Furthermore, doing nothing is good if done for a good reason, and evil if done for an evil reason. There is no single answer, because it is a hypothetical and morality requires judgement of the particular circumstances and the scenario is contrived and does not exemplify any single moral principle well: one can interpret it in different ways.