In Philippa Foot's essay "The Doctrine of Double Effect," she discusses various cases that present a choice between the death of one person or the death of five. She examines these situations under the lense of the doctrine of double effect (DDE), which essentially contends that an action can sometimes be morally permissible even if it results in bad, unintended consequences. One of the cases she discusses is that of a patient who is in need of a massive dose of a certain drug in order to save his life. There is a limited supply of this drug and there are five other people who are also in need of a dose. These five patients do not require as large of a dose as the first patient, in fact, their lives can all be saved by the same amount of medicine that the first patient would have to consume in order to survive. In this case, it would make sense that the right decision would be to spare the five patients and give them the last supply of the scarce drug. Therefore, it is more permissible to allow one person to die, rather than five. .
Foot contrasts this example with a similar premise, except that in this scenario a doctor is able to save the lives of five patients in need of organs if he decides to sacrifice one healthy patient to use his kidneys, lungs, and heart. If you examine this case the same way as the previous, then it would seem to suggest that the doctor would be right in killing one patient in order to save five. However, it is here that Foot points out the deontological principles of positive and negative duties. Negative duties refers to "obligations to refrain from such things as killing or robbing" (Foot 96), whereas positive duties would be obligations to do positive things, like giving to charity. Foot argues that this distinction between positive and negative duties supports why different situations of saving one person vs. saving five result in different perspectives of moral permissibility.