It's a sad day for horse lovers. Barbaro, the magnificent thoroughbred who broke his leg two weeks after winning the 2006 Kentucky Derby (I watched both races live), was put to death after taking a turn for the worse in his recovery. See here for the New York Times story. Barbaro's killing is a case of euthanasia. The word "euthanasia" means good, gentle, or easy (eu) death (thanos). It may sound odd that there could be a good, gentle, or easy death, since death destroys the possibility of enjoyments, activities, projects, and experiences, which give our lives value and meaning; but if one's life is racked with pain and there is little or no prospect of recovery, death can seem, and be, preferable. The paradigm case of euthanasia is where a sentient being is terminally ill, will die soon anyway, and is in great pain. Death is a release or escape from this predicament. Euthanasia is often called mercy killing, for obvious reasons: Its motive is mercy. It is done for the sake of the being who is killed, rather than for the sake of some other being or beings or of society generally.
You've probably heard the word "euthanasia" applied to dog pounds. But this is inappropriate. Many or most of the dogs who are put to death in pounds are perfectly healthy. They are not terminally ill; they will not die soon anyway; and they are not in pain, much less in great pain. They are killed not for their sake but because society is unwilling to provide for them. (Don't confuse society with government. This is not a call for greater taxation, which is coercive and therefore presumptively wrong.) I'm not saying it's wrong to put such animals to death. That's a debatable issue. I'm saying that, if we do put them to death, we shouldn't call it euthanasia, for that implies something false, namely, that the killing is done for the sake of the animal. It's convenience killing, not mercy killing. How would you like to be killed out of convenience to others?