Daniel Callahan, PhD, Director of International Programs at the Hastings Center, wrote in his 1995 article "Vital Distinctions, Mortal Questions: Debating Euthanasia and Health Care Costs" that appeared in the book Arguing Euthanasia that:

“The distinction between killing [active euthanasia] and allowing to die [passive euthanasia] is still perfectly valid for use… The distinction rests on the commonplace observation that lives can come to an end as the result of (a) the direct action of another who becomes the cause of death (as in shooting a person), or as the result of (b) impersonal forces where no human agent has acted (death by lightning or by disease)…

At the center of the distinction between killing and allowing to die is the difference between physical causality and moral culpability. On the one hand, to bring the life of another to an end by an injection is to directly kill the other–our action is the physical cause of death. On the other hand, to allow someone to die from a disease we cannot cure (and that we did not cause) is to permit the disease to act as the cause of death.”