The Plank and Double Effect

Doctrine of Double effect

It is morally permissible to perform an action with bad effects (e.g. killing one person to save another) iff:

 1. The act itself, considered in independently of its effect, is not wrong.
 2. Only the good effect is directly intended (the bad is merely foreseen).
 3. The bad effect is not a means for achieving the good.
 4. The good effect outweighs the bad

In a nutshell: An act is not permissible if the intention is to do a bad thing to achieve a good consequence of that bad thing. But an act is permissible if the intention is to do a good thing that simply has bad consequences (outweighed by the good).

Double effect in action


1. Dropping a bomb on a military base, knowing it will result in hundreds of civilian deaths. But the destruction of the base will end the war, resulting in many more lives saved.

2. Dropping a bomb on civilians, resulting in hundreds of deaths, the resulting terror leading to surrender and many more lives saved.

Notice the consequences are identical. According to Double Effect 1 is permissible but 2 is not. Many find this intuitively right. Now consider...

The Plank

Case 1

Two unconscious men are lying at either end of a plank suspended from a runaway balloon by a fraying rope that will soon break, plunging both men to their death. The plank passes a window. You can save one man by grabbing him. But that will tip the plank and kill the other. What should you do? Grab one man and you save him. But as a result of your action the other will immediately die. Or do nothing, and they will both soon die.

Intuitively, it seems right to me to save one even if as a result the other immediately dies. It seems right to kill an innocent person so that a life might be saved.

Doctrine of Double Effect concurs. But now consider...

Case 2

Two unconscious men are lying at either end of a plank suspended from a runaway balloon by a fraying rope that will soon break, plunging both men to their death.

The plank passes your window. You can save one man by firmly shoving the other, nearer man off the plank to his death (he is far to heavy for you to grab). Shove him off and the plank will tip and the other man will drop safely onto an adjacent roof. Do nothing and both men die. What should you do?

Intuitively - push the man to his death. In Case 2, it also seems right to save one man by directly and intentionally killing the other (his death is not an unintended but foreseen bad consequence), just as in Case 1. But Double Effect says you should not shove the man off the plank. You should do nothing, with the result both die.

But does it really make any moral difference that one is grabbing a man rather than shoving him off? Isn't this difference morally irrelevant?


Patrick said…
Slightly different question: I've always had a vague feeling that the doctrine of double effect was a method for deontological moral systems to mimic the effects of utilitarianism. Does that match your impression?
In Case 1, you have saved a life.

In Case 2, you have actively murdered in order to save a life.

What it boils down to is this:

Saving a life - moral
Death occurring - unfortunate
Murdering - immoral

In case 1, a moral action is taken with an unfortunate consequence.

In case 2, the action taken is immoral with a moral consequence.

I guess what the Double Effect principle is saying, then, is:

Moral + Unfortunate > Immoral + Moral

No wickedness/evil/badness/immorality occurs in Case 1, whereas some does in Case 2. I guess the Doctrine of Double Effect strives for absolutely no immorality to occur.

So, to answer your question directly: There is a moral difference, in that one act is partially immoral (case 2) whereas the other isn't at all, so it's morally better (case 1).

Oh, I think I'm forgetting something. The Double Effect would have you, in the case of Case 2, let both die.

So what the Double Effect is also saying is:

Unfortunate + Unfortunate > Immoral + Moral

In the case of letting them both die (let's call this Case 3), there is still a lack of wickedness/immorality. Case 2 is partially evil; Case 3 is wholly unfortunate.

So, yeah, there is still a moral difference. Case 1 is the most moral - doing a moral action with an unfortunate consequence. Case 3 is the middle ground - allowing two unfortunate events to occur in order to avoid acting immorally. Case 2 is morally the worst - having murdered, acted immorally, in order to bring about a moral consequence.

That conclusion may seem cold, but... is it colder to murder an innocent or to (knowingly) allow an innocent to die? Is it worse to commit a man to death undeservedly or for a man to die of causes unprovoked?
Rob A said…
When you grab Man 1 you are saving the life of the individual you are acting on. When you push Man 2 you are ending the life of the individual you are acting on.
Ron Murphy said…
Hi Stephen,

I think case 1 is mistaken in the way you express it.

"But at the price of killing the other."

How are you 'killing the other' and what way is it the 'price'? He was going to die anyway, so you're not killing him, and nor is it an 'additional price'.

If your thought experiment allows some chance possibility of them both being saved moments after you grab your man, then maybe you are 'killing' the second man. But without this possibility you have only added good, by saving one man. The loss of the second is no different.

And the only significance in case 2 is that you are being more active in the event - and then only because you have changed the conditions of the thought experiment, by introducing the ledge and the weight of the first man.

So, given how difficult it is to make these decisions objective (e.g. to the extent of being numerically measurable) then the changes you have introduced outweigh any significance in moral difference.

Therefore I'd say they are both of equal moral value, in as much as we can measure moral value, because in both you have saved a life that otherwise would have been lost.
Stephen Law said…
Ron - you are right - in fact I had intended to change the wording of case 1, and have now done so. Thanks... Stephen
Stephen, your whole example is horribly wrong.

Firstly, all acts of war are unjustifiable acts of wanton mass-murder. You cannot justify dropping any of the bombs. There is no such thing as military and civilian targets. These are lie-based and illegitimate societal constructs. They are simply BOTH human targets of a murder act.

Ending a war is ridiculous, because the act of bombing IS war. Society engaged in that war.

I have a suggestion, Stephen:
What about making a case of abortion clinic killer Peter Knight of australia vs society's stance on child-murder via abortion? Now there is a great example of the concepts!
@Stephen law. (Private)

By the way, Stephen you have failed to step-up and defend your society against My Forbidden Truths. still stands

wombat said…
A rather prescient blog post in view of the furore over a real life situation in which only one of two lives could be saved. You probably spotted it on Ophelia Benson's site but just in case.


and for one religous take on it.