The Doctrine of Double Effect: Interpretations, Application & Criticisms

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  • 0:01 Doctrine of Double Effect
  • 1:02 Formulation and Interpretation
  • 2:32 Applications of Double Effect
  • 3:42 Criticisms of Double Effect
  • 4:33 Lesson Summary
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Lesson Transcript
Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

Actions have consequences, this we know. But how do we separate permissible and impermissible consequences? Explore the doctrine of double standard, and test your understanding with a brief quiz.

The Doctrine of Double Effect

Our actions have consequences. We've all been pretty aware of this basic fact since the first time we were grounded. And the first time we failed a test after not studying for it. And dozens of other times throughout our lives, really. Actually, we're constantly learning this lesson.

But, sometimes actions have consequences that we weren't expecting. Where do these fit into our moral compass? When you do something, knowing that the consequence won't be great, you take on the responsibility for that action. Is the same true of unintended consequences? Well, according to the doctrine of double effect, it can be permissible to cause harm if the harm is a side effect of an action whose main intent was meant to bring about good. This side effect is also called a 'double effect.' Great. Actions have consequences, but as it turns out, we may only be responsible for the main ones.

Formulation and Interpretation

The doctrine of double effect is usually credited to the 13th-century Catholic priest Thomas Aquinas, who claimed that it was permissible to kill someone in your own self-defense, but only if you did not mean to kill that person. And that's been the basic idea ever since. You meant to do something positive, like defend yourself, but that action created an unexpected negative side effect.

Since the main intention was good, the side effect is excusable. But, according to Aquinas, this is only true as long as the total outcome is positive. In Aquinas' example, a negative total outcome could mean using more force than is necessary to defend yourself. The negative side effect is no longer excusable since a positive result could have occurred without it.

In the modern moral world, the doctrine of double effect is still used by the Catholic Church, provided that an action meets four very specific criteria:

  1. The action must be morally good.
  2. You must not desire the negative consequence, and if you can produce a good result without any negative consequence, then you should.
  3. The good effect must be as immediate as the negative effect.
  4. The good effect has to be good enough to make up for the negative effect.

If all four of these criteria are met, then the negative outcome was permissible, and you're not morally responsible for it.


Okay, let's look at a few applications here. How about warfare - that's a common area where this is applied. If an army tries to kill civilians in order to weaken the rebel army, that's not okay. The army in this case meant to kill civilians. However, if the army decides to tactically destroy a military target, even with the knowledge that civilian causalities could occur, the main intention is destroying a building. So if people are killed, that's permissible, because it was never the intended consequence.

How about another example, maybe more from daily life? What if you saw someone robbing a store? Yes, you could smash the window and cause lots of property damage trying to stop the thief, but in that case, the negative outcomes would be intentional. Now, if you tried to stop the thief by simply making him aware of your presence, and he smashes a window to escape, that consequence was unintended, so it's permissible.

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