When we stand to affect another person or animal, at least four moral considerations seem potentially relevant:

1. The creature’s suffering or distress versus its happiness, contentment, or satisfaction.
2. The creature’s sense of meaning, purpose, and agency.
3. The creature’s ability to live in its natural way or to be itself. And …
4. The impact on other creatures that know and care about the creature that we are directly affecting.

The first consideration is relevant to all sentient beings in proportion to their capacity for sensation and experience. Perhaps a clam cannot suffer appreciably. But there is no reason to think that we human beings are the most sensitive of all creatures–or at least, not by much. And since the first consideration applies to most other animals, it is wrong to reduce their happiness or increase their suffering.

A more difficult question is whether a sudden and painless death reduces happiness. On one account, the net of a creature’s happiness accumulates like a running tally over the life-course. In that case, a painless death freezes the score permanently in place, which can make the total higher than it would have been if the future would have been less happy than the past was. A different views is that a creature has no happiness or suffering at all after death, and therefore death has no impact on happiness. In Epicurus’ phrase, “Death is nothing to us.” I am dissatisfied with both views but not sure that I have a better proposal. Certainly, happiness has a temporal aspect, because suffering on one day lingers on the next. But I struggle to say what impact ending a life has on the creature’s happiness.

The second consideration depends on an ability to make meaning or sense of one’s life and to make consequential choices according to one’s sense of purpose: in a word, “agency.” I am not committed to the premise that agency is a capacity of human beings alone, but we certainly have a very advanced version of it. Note that this capacity is temporal: we make meaning by putting our present state and our current choices in a longer narrative that includes a past and a future. One reason that killing a human being is badly wrong is that it ends the narrative that the person is constructing and thereby destroys her agency. I don’t think the same argument applies to the instantaneous and painless termination of the life of a chicken.

The third consideration–naturalness–seems to apply most to creatures that are not human beings. If possible, a bear should be left alone to live as a bear. Our family dog would not be better off if he were left in the woods to fend for himself like coyote, but he should be able to live the life natural to a domesticated dog, with activities like walks and cuddles. And as for a cow–I am inclined to think that its natural state must include time grazing in a field and nursing a calf. I am not sure that suddenly being slaughtered violates its ability to live a natural life. That means that factory farming is unacceptable but family farming may be consistent with respecting the natural states of farm animals.

As for human beings, we are also natural creatures in the sense that we are an evolved species with many innate limitations and tendencies. But we are capable of reflecting on the whole range of our inherited traits and distinguish the better from the worse. We have a natural proclivity to altruism but also to aggression, even to rape and murder. For us to live according to nature is not nearly good enough. We build institutions and norms to change our inherited natures for the better. That forfeits a right to live naturally and makes the third consideration irrelevant to us.

The fourth consideration applies to any animal that cares for another. In the old Disney cartoon, the death of Bambi’s mother deeply hurt Bambi. Although the cartoon anthropomorphized its animal characters, Bambi’s emotional reaction seems plausible enough for a deer. Still, people may be unique in that our relationships with other people are mediated by language and other forms of communication. We can suffer–or have our sense of purpose and agency frustrated–by learning of the death of someone we have never even met. In contrast, if Bambi had not directly experienced his mother’s death, he wouldn’t have suffered from it.

Freedom is certainly a moral consideration as well, but for human beings, it has a lot to do with #2 (purpose and agency), whereas for animals, it is related to #4 (naturalness). For a person, to be free is to be able to live according to her own sense of purpose. But a bear is free if it’s left alone to be a bear.

What all this means: Intentionally causing the suffering of another creature is always wrong, albeit a wrong that should be balanced against other considerations. Reducing the ability of a non-human creature to live naturally is also a wrong, at least ceteris paribus. But that is a complex question when it comes to farm animals. Killing a person is a special evil because it not only causes suffering but it ruins the purpose and agency that came from that person’s ability to plan and foresee the future. Furthermore, the impact on other human beings of killing a given person is particularly deep and widespread. This is one reason that it is badly wrong to kill even a human being who does not have much agency, such as a neonate. Killing an advanced animal painlessly and suddenly (beyond the sight of its kin) does not necessarily violate considerations #3 or #4. It may violate #1, depending on how we understand the temporal dimension of happiness and suffering. And it may violate #2, but only to the degree that other advanced species have capacities for long-term planning.

See also my evolving thoughts on animal rights and welfare.