Double Effect reasoning?


Edumacate me! (please)

  1. What impact does double effect reasoning have on Catholic theology?

  2. What is the difference between “intended” and “merely foreseeon” consequences?

Recently a fellow Catholic told me that double effect reasoning justifies the use of contraceptives when one partner has an STD. He claimed that the “intended” effect was the prevention of the spread of disease, while the elimination of the procreation from the act was “merely foreseen.”

So… is double effect a valid form of reasoning? What prevents one from arbitrarily picking which consequence is intended and which is merely foreseen?


The most common example of use of the principle of double effect I’ve seen is ectopic pregnancies, in which the embryo implants inside one of the fallopian tubes. It is fatal if not treated. The only way to fix it is to remove the tube, which has the side effect of killing the embryo; however, the purpose is not to end the pregnancy but to save the mother’s life.

I don’t think many people here will get behind the idea of using prophylactics to lower the risk of STD transmission during sex, however much sense it might make.


Your friend does not have the whole principle at work here in the comment that double effect allows the use of contraceptives when STDs are involved.

There are four conditions that need to be met for a valid case of Double Effect. If any one of the conditions is not met then the principle of Double Effect can not apply.

Here are the conditions.
*]The action itself must be morally good or indifferent, never evil.
*]The good effect must not be obtained though the evil effect, i.e. by means of the evil effect.
*]The evil effect must not be intended, but only tolerated.
*]There must be a sufficiently serious reason to justify allowing the evil effect (proportionality test).[/LIST]So in light of these conditions lets examine the use of contraception in the case of STDs.

The action is the use of contraception, the evil effect is the sex act not being open to life, the good effect is not passing on the STD.

Condition #1 fails immediatly as the useo f contraception is morally evil, not good or even indefferent.

So we could stop here but lets go on for the exercise.

Condition #2 passes as the good effect is not obtained by the evil effect but it is not assured as contraception is not 100% proof against passing on STDs.

Condition #3 passes as the evil effect is not intended.

Condition #4 fails as having sex is not a serious reason to justify using the sex act in such a way that it is not open to life.

The Catholic Church has ruled on this by saying that condom use is not justified in the case where one of the partners is infected with HIV.

This is because it is not open to life and it is not 100% effective.

Hope this helps.


Thanks a heap! The definitions I had been reading did not include all of these criteria. It makes MUCH more sense to me now. :smiley:


I think of it this way–we can never use evil means to achieve a good end. What we can do is use good means to achieve a good end even if there is an unintended evil side-effect.

For example–the ectopic pregnancy. The means–surgically removing a hazardous body part–is licit. The end, saving the mother’s life, is licit. The evil side-effect is the death of the embryo.

Let’s look at your friend’s example. The end is the prevention of the spread of the STD–a licit end. The means is using condoms. An illicit means. This is a case of the end not justifying the means, not an example of double effect.


While this is a quick short hand way of determining Double Effect it lacks the proportionality test, which is very important. Such as when there is a drug that a woman can take that can help out some illness she has but will cause serious defects or even death to her unborn infant. If her illness will not cause her death then it is not a case of Double Effect becuase the proportionality test will fail.


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