Consider the ethics of imagined controlled experiments assessing the effects of smoking and heart and lung disease or child abuse and later personality development. Conducting experimental research would require that we recruit subjects, for example, teenage non-smokers or unabused children, and separate them into two groups, a control group and an experimental group, then see to it that the non-smokers in the experimental group take up cigarette-smoking to some particular level (e.g., heavy, moderate, or light), periodically verifying they are continuing to smoke while we monitor them for onset of disease or that we arrange for the abuse of the children in the experimental group and subsequently compare them with the controls on personality variables.

To act thus would be unethical in that, not surprisingly, we can have a good degree of certainty that we would be exposing the non-smokers and the children to serious harm, even though we may not be able to precisely specify how much and which individuals would be most badly affected.

Before research can begin as part of the planning process there is a decision to be made as to whether the benefits of any particular study outweigh the risks. In the imaginary case above the construction of the proposed experiments actually requires harm to be undergone by research participants. This presumes that we should consider that such voluntary (and preventable) infliction of harm to be unjustifiable in the circumstances, and that this harm could not be mitigated or excused by what we might learn from the exercise.