Because most philosophies that frown on reproduction don't survive.

Wednesday, August 22, 2007

The Limits of Double Effect

For those who aren't Catholic moral theology geeks (really, some people don't spend their spare time this way?) the "principle of double effect" goes like this: It may in certain circumstances to do something which has a result which would normally be a sin, if your object in performing this act is some other good of which the bad results are a foreseen but unintended side effect.

The classic example is, in a case of a falopian pregnancy (something which often fatal to both mother and child, and from which the child is pretty much guaranteed to die) it is possible to remove the falopian tubes in order to save the mother's life. This has the foreseen side effect of the unborn child dying, since the tubes in which the child has implanted are removed. However, it is not considered as a similar moral act to an abortion because the object is to remove the tubes and save the woman's life, not to kill the child.

Now, I think it's pretty clear to anyone that this is a useful form of moral thinking. Many acts have consequences (known or unknown) that are not what we intend. And I know that I've seen a few people (generally in mentally vulnerable times like late high school) get themselves all tied up in knots of paralyzing worry over what the unforeseen results of their actions might be.

However, just as the possession of a good hammer does not turn everything into a nail, so the possession of a fun piece of moral reasoning does not mean that it should be applied everywhere. Case in point, I recently heard someone argue that it is inherently immoral for a soldier or police officer to intentionally use "lethal force". Rather, this fellow argued, that such a person uses force in order to achieve an objective (self defense, defending another, etc.) and might as a result "accidentally" kill his opponent.

Now, I understand what he's getting at here. Standard US rules of engagement specify that shooting an armed opponent is acceptable, finishing off a successfully neutralized wounded enemy with a shot to the back of the head is not.

But I think that attempting to use the principle of double effect in this kind of situation is deeply misguided. Attempting to argue that someone who sends a number of metal slugs in the direction of another human being at over a thousand feet per second doesn't mean to do them harm is just plain unrealistic. And by making the argument, I think one fails to deal with the moral facts of the issue and makes moral theology sound foolish into the bargain.

It seems to me that the argument that should instead be made is that certain circumstances justify the taking of life -- to the extent necessary to resolve the circumstance. A soldier, policeman, or an ordinary citizen defending his family may need to use lethal force against an aggressor in order to preserve his life or the lives of others. The taking of life is justified by the situation to the extent (and not beyond the extent) necessary to achieve that objective.

In that sense, the use of lethal force is a matter of justice. However, as Christians we believe that justice and mercy must always go hand in hand. And there is indeed a place where mercy kicks in.

While justice sometimes makes the use of lethal force to achieve some good necessary, mercy emphasizes the difference between the person and the objective. The enemy who is no longer in a position to threaten you must cease to be an enemy. The justification for using lethal force is gone when the objective is achieved.

Operationally, this may not be terribly different from the double effect explanation. But I think it is much more intellectually honest and morally sound.


Pro Ecclesia said...


Thank you for your common sense, as well as your uncommon ability to engage in moral reasoning, to think through these sorts of issues, and to put your reasonable thoughts to writing in a manner that is easily read and understandable.

The problem you address arises whenever someone seeks to impose a moral philosophy - in this case, the "principle of nonviolence" - that is not mandated by our Faith. The Church has a Just War Theory for a reason. The Church permits self-defense and defense of others for a reason. The Church has historically allowed and even imposed the death penalty for a reason. There are instances where the Church recognizes that taking the life of another is necessary to preserve the moral order. The principle of double effect is neither necessary nor useful in these situations.

Certainly, the Church allows for pacificism and nonviolence as legitimate options for Catholics, but it does not demand them as the only permissible options, as some would have us believe.

Darwin said...

Yeah, I think what we're seeing here is an attempt to provide moral reasoning for traditional Catholic moral teaching which effectively contradicts the teaching itself. It makes an attempt to fit, but in the end it's not a good one.

All of this boils down to the tendency of people to equate "thou shall not murder" with "thou shall not kill".

Kate said...


I was about to add the distinction between "kill" and "murder", but I see you beat me to it. Proportionality is then the guiding principle in the use of force to protect ourselves and others, which you touch on very nicely in this post.

Anonymous said...

When I was in the army in my mispent youth I was taught not to shoot at anything living that I did not intend to kill. The idea that it is immoral to kill an enemy soldier intent on killing you would have struck my instructors as farcial, and I certainly agree with them.

Anonymous said...

That's quite an attack on PDE (Principle of Double Effect). The words you use: "geeks", "fun piece of moral reasoning", "deeply misguided", "makes moral theology sound foolish", and then describing your method as "much more intellectually honest and morally sound". Hmmm.

Are you sure that you are not just taking a single relatively simple situation (lethal force as a means of self defence), with a fairly obvious answer, choosing to analyze it in a different way, and then deciding that the PDE (Principle of Double Effect) must surely be a horribly bad thing?

The description you give of how the PDE works in this kind of situation is entirely correct moral reasoning (and has been since at least Aquinas), though it could definitely benefit from being stated in a more careful and more expanded way. (The number one problem with explaining things with the PDE that I have experienced is that people are too sure they know exactly what every word means: in particular, the word "intend" all too easily and unhelpfully slides around in meaning and usage.)

You say: "While justice sometimes makes the use of lethal force to achieve some good necessary, mercy emphasizes the difference between the person and the objective. "

That's a use of 'mercy' that I don't understand. I would understand mercy as some good action performed out of love, rather than from justice or obligation or compulsion. In which case, taking into account the difference between the person and the objective is still definitely in the realm of justice.

(Mercy could come in to self defence, for example, if I chose a method of defending myself that was a bit more likely to leave my assailant alive, but at the cost of some extra risk to myself.)

Pro Ecclesia said...


Your response is one of the single most disengenuous things I've ever read in blog comments.

An "attack" on the principle of double effect? Where did Darwin ever say that "the Principle of Double Effect must surely be a horribly bad thing"?

Did you bother to read what Darwin wrote, other than to pick out a few buzz words to put in scare quotes?

Darwin makes it plain that he thinks the principle of double effect is a GOOD thing: "I think it's pretty clear to anyone that this is a useful form of moral thinking". He just thinks it's ill-suited when applied to things like self-defense. It wasn't Darwin who chose to talk about double effect in relation to self-defense and defense of others; it was another blogger at another blog. Darwin was merely responding to the inappropriate application of double effect in that instance.

I'm going to give you the benefit of the doubt and assume you didn't deliberately twist what Darwin wrote. Instead, I will encourage you to work on your reading comprehension skills.

Darwin said...


First, I think perhaps I wasn't entirely clear (or you somewhat misread my intent), in that my intention is not at all to attack the principle of double intent as a whole. (Moral theology geeeks was intended as a self-identifier, not an epithet.)

My problem with the application to just war/self defense situations is that it seems to me that there is no real other objective. Maybe this is something that's been overly drilled into me as a result of spending so much time in the gun culture, but you absolutely do not shoot at or even point a gun at a person you don't intend to kill. So the idea of "I was only intending to defend myself, not to use lethal force" strikes me as mischievious pedantry.

Thinking about it more, I think the reason this doesn't fly as double intent is that there isn't a real distinction between the intended object and the forseen but "unintented" result. It feels too much to me like explaining imprisonment as a punishment by saying, "It's always wrong to imprison another, but in putting someone in jail for murder we don't intend to imprison him but merely to keep him from committing more murders -- of which his imprisonment is a forseen but unintended side effect."

Double effect suggests having one object which necessarily results in an additional effect other than the one that is your object. But in this case, there's really only one object: using force to stop an agressor.

On the justice/mercy comments, I think I maybe threw my terms around a bit too much. I think I was seeing mercy as being the opposite of vengence in this situation. Vengence being an identification of the person with the object such that one attacks the person even after the object (neutralizing the threat they represent) is no longer in place. I don't know if "mercy" is the right word, but I was wanting to contrast that with the necessity of seeing the enemy as neighbor in need of help the moment that he ceases to be an active threat.

bearing said...

(By the way, for clarity, you should correct your line "it is possible to remove the fallopian tubes" to "tube" -- the mother of an ectopic embryo only need lose one tube, not both -- her fertility is thus impaired, not destroyed, by the procedure)

Darwin, I would phrase it like this. It's obvious that the Principle of Double Effect isn't what justifies lethal force in the soldier situation because the harming of the "bad guy" isn't a "side effect" of an action that does good. Rather, the good is achieved through the means of harming the bad guy enough to put him out of business, so to speak -- in colder words, "neutralizing" him. If you can do it without killing him, great, but often that's not possible. Getting that bad guy out of operation is truly the objective. (Now, if we considered that to be inherently evil, then it wouldn't be justifiable for any end. But we don't.)

With the ectopic pregnancy, as with many situations when pregnancy of some kind is threatening the mother, the death of the child is not the means by which the end of rescuing the mother is achieved, as if we could save her through some magic involving infant sacrifice. Removing the Fallopian tube will save her (though the child will die). The medical option of performing an abortion, then, becomes "kill the child to save the Fallopian tube and the extra cost of the salpingectomy," not "kill the child to save the mother."

A much more difficult dilemma (they do say that hard cases make bad law) is the far-rarer case of an ectopic pregnancy in which the embryo has attached to a vital, non-removable organ rather than the fallopian tube.

Anonymous said...


(N.B. in what follows, I certainly know that you do understand the morals of the situation. The problem lies in choosing the most clear form of words for expressing it.)

Although your intention was not to attack the PDE (Principle of Double Effect) as a whole, I think that the particular objection you make would in fact have exactly that effect. Hence my great worry.

Imagine this situation: Someone who is known to profoundly hate me grabs a knife and starts to walk towards me, saying: "I'm going to kill you!". I ask somebody nearby, "Is it OK for me to defend myself by killing him?", and I get the reply, "Yes." So I go ahead, take out my gun, and shoot two bullets into my assailant's head, causing him to fall to the ground, motionless. (Call this Action X1). I then go up to my assailant and, without checking his pulse, chop him up into one-inch cubes, and dissolve the cubes in acid. (Call this Action X2).

Now, in whatever form of words might be chosen, there is a distinct moral difference between Action X1 and Action X2 -- since X1 is permissible, but X2 is not. But this means that simply saying "Yes, it's OK to kill him," is radically insufficient to capture the exact moral situation. Or, saying, "I intended to kill my assailant" similarly doesn't capture the distinction that X1 is permissible, but X2 is not.

The PDE can be used to actually capture this distinction. I don't see what you propose to replace it with.

Darwin said...

I guess what I'm trying to do is draw a distinction between the assailant and the person who assails.

One is justified in killing an assailant, but since an assailant is definitionally someone who is actively attacking you, once his attack ceases you are no longer justified in harming him.

So I'm agreeing that the acceptibility of using force against the assailant only holds as long as his attack does -- but I don't think it works to say that the act of force against him is in any sense only forseen but not intended.

I guess I'm instead thinking in somewhat Aristotelian terms in wanting to say: You may kill an assailant -- however one who is no longer attacking you is categorically not an assailant, and thus no longer falls under the previous ruling.