Intuitive illustrations of the Doctrine include (adapted from (McIntyre, 2011)):
1. In a military campaign, it is typically judged impermissible to target civilians, but it is often judged permissible to target a legitimate military target (e.g., a WMD factory) even if the attack on the military target is foreseen to lead to civilian causalities.
2. Someone who thinks abortion is wrong, even in circumstances that would save the mother’s life, might nevertheless consistently believe that it is permissible to perform a hysterectomy on a pregnant woman with cancer, even if it is foreseen that the hysterectomy will lead to the death of the fetus.
However, as Levy points out, there is a great deal of evidence suggesting that if one judges an effect to be morally bad, it is more likely that one will judge the act to have been brought about intentionally (and, thus, not merely foreseen). Much of this evidence comes from a series of studies conducted by Joshua Knobe and others (for an overview see: Knobe, 2010). In the earliest of these studies, Knobe (2003)randomly assigned participants to read one of two stories about a chairman of a company who instituted a new profit-generating program. The only difference between the two stories was that the foreseen side effect of the program would either harm the environment (a morally negative outcome) or help the environment (a morally positive outcome).
The harm version read as follows:
The vice president of a company went to the chairman of the board and said, “We are thinking of starting a new program. It will help us increase profits, but it will also harm the environment.”
The chairman of the board answered, “I don’t care at all about harming the environment. I just want to make as much profit as I can. Let’s start the new program.”
They started the new program. Sure enough, the environment was harmed.
The “help” version was identical to the “harm” version except ‘harm’ was replaced with ‘help’.
After reading the stories, participants were asked if the chairman intentionally harmed [helped] the environment. What Knobe found was that the vast majority of participants were willing to say that the chairman intentionally harmed the environment, but very few were willing to say that the chairman intentionally helped the environment. These findings have led Knobe and others to claim that judgments of intentionality are sensitive to moral considerations. This pattern of asymmetrical attribution of intentionality (and other state-of-mind attributions) based (ostensibly) on manipulations of moral considerations has become known as the side-effect effect, or the Knobe effect.
If Levy’s construal of the Doctrine are correct, and if people’s judgments of intentionality are sensitive to moral considerations, then the Doctrine of Double Effect is circular and would be an unreliable guide for grounding judgments about the permissibility of actions.
For example, if one already thought bringing about civilian causalities was impermissible, then one would be more likely to judge that the foreseen bringing about of civilian deaths was intentional, even in cases where the bringing about of civilian deaths was a side effect of attacking a legitimate military target. Since the civilian deaths would be judged to be intentional, according to Levy’s construal of the Doctrine of Double Effect it would be impermissible to attack the legitimate military target. Impermissibility judgments feed into intentionality judgments which feed back into impermissibility judgments. Thus, the Doctrine is circular and question-begging!
However, the Doctrine of Double Effect is not always primarily construed as depending on the distinction between intentionally bringing about an outcome versus merely foreseeing an outcome will be brought about. Rather, under many traditional formulations of the Doctrine of Double Effect, the morally relevant distinction depends primarily on whether an act or outcome is a side effect or a non-side effect (i.e., means or a goal).
To build an even stronger case against the Doctrine of Double Effect, one would also need evidence that people more readily construe bad outcomes as non-side effects. To the best of my knowledge, there is currently no published study that shows that moral considerations can affect people’s classification of an outcome as being a side effect or a non-side effect. However, my lab is currently exploring just this possibility, and the early results are in: it looks like moral considerations do have an impact upon whether people classify an outcome as a side effect or a non-side effect.
For example, we find that people overwhelming (about 82%) classify HELPING THE ENVIRONMENT in Knobe’s helping the environment version of the chairman case (see above) as a SIDE EFFECT. However, only 42 percent of people classify HARMING THE ENVIRONMENT in Knobe’s harming the environment version of the chairman case as a side effect.
To make sure this finding was not simply a consequence of the exact details of Knobe’s chairman cases, we also tested seven other cases that were modeled on Knobe’s chairman cases.
For example, in one of the cases, a scientist (instead of a chairman) is deciding whether to implement a new methodology (instead of a new program) that would help her get the results she wanted (instead of generating more profits). In one version of the story, the new methodology would also violate ethical guidelines (instead of harm the environment), and in the other version of the story, the new methodology would also conform to ethical guidelines (instead of help the environment).
In another example, a ship captain is deciding whether to take a new route that would help her arrive at the destination quicker. In one version of the story, the new route was a dangerous route and thus would put the crew into extreme danger, and in the other version of the story, the new route was a very safe route, allowing the safety of the crew to be ensured. Same basic structure of Knobe’s original chairman case, but the actor and outcomes were varied.
What we found was that in six of the eight cases (including Knobe’s chairman case) people were more willing to say that the bad outcome was not a side effect than they were willing to say that the good outcome was not a side effect. To put this differently, when the outcome was good (e.g., helping the environment, conforming to ethical guidelines, ensuring the crew’s safety), people overwhelming judged the outcome to be a side effect. But when the outcome was bad (e.g., harming the environment, violating ethical guidelines, putting the crew into extreme danger), people tended to be split on whether the outcome was a side effect or a non-side effect.
Thus, our initial evidence suggests that people’s classification of outcomes as side effects or non-side effects may, in part, depend on moral considerations.  If this is right, then even when construing the Doctrine as being primarily concerned with the distinction between side effects and non-side-effects, the evidence suggests that the Doctrine of Double Effect is circular and would be an unreliable guide for grounding judgments about the permissibility of actions.
Want to cite this post?
Shepard, J. (2012). Experimental Ethics: An Even Greater Challenge to the Doctrine of Double Effect. The Neuroethics Blog. Retrieved on , from http://www.theneuroethicsblog.com/2012/08/experimental-ethics-even-greater.html
 While it is true that talk of intentions is present in almost all discussions of the Doctrine of Double Effect (even those that construe the primary distinction as side effects versus non-side effects), I take it that discussion of intentions play a role in the Doctrine in so far as intentions are a guide to distinguishing what outcomes should count as side effects versus non-side effects.
 In my view, technically, people’s asymmetric classification of outcomes as side effects/non-side effects is not dependent on moral considerations, but rather is dependent on a non-moral considerations that typically (though not always) correlate with the evaluative valence of an outcome. Getting into the details of my view is beyond the scope of the post and is unimportant for the particular point at hand. (It would turn out on my view that the Doctrine would be circular for a large portion of cases due to the nature of the correlation between the non-moral considerations and evaluative outcomes.)
Knobe, J. (2003). Intentional action and side effects in ordinary language. Analysis, 63(3), 190–194.
Knobe, J. (2010). Person as scientist, person as moralist. The Behavioral and brain sciences, 33(4), 315–29; discussion 329–65.
Levy, N. (2011). Neuroethics: A new way of going ethics. AJOB neuroscience, 2(2), 3–9.
McIntyre, A. (2011). Doctrine of double effect. Stanford Encyclopedia of Philosophy. Retrieved from http://plato.stanford.edu/entries/double-effect/
Sinnott-Armstrong, W., Mallon, R., McCoy, T., & Hull, J. G. (2008). Intention, temporal order, and moral judgments. Mind & Language, 23(1), 90–106.