Campbell, in my view rightly, rejects the proposed dichotomy between two kinds of grounding. I’d be inclined to say: to think of grammar and of human nature as somehow offering parallel modalities – each setting its own kind of limit to what is possible in moral thought – is confused. Indeed, I’m not even clear what it would be to think of the two sentences above, taken in isolation, as expressing either an empirical claim or a point of grammar. Deciding whether someone loves evil (or cow dung) is not like establishing whether someone is allergic to fish roe. For one thing, the terms of the relation, “fish roe” and “allergy” are distinct. But love and its object cannot in this way be thought of separately. How love is expressed, what it demands of us, is dependent on the object of love. To show my love of someone is to show my understanding of her.
It is also unclear under what aspect a person might be taken to love evil. Does he love evil for its own sake (e.g. a sadist, a person embittered by life, someone in the grip of vindictiveness, etc), or for what he hopes it will bring (e.g. a terrorist)?
For another thing, and connected with this, we are acquainted with the kinds of context in which food allergies are spoken about, the reasons for being concerned about it, the practical consequences. But when the philosopher raises the question whether it is possible or impossible to love evil, there is no context enabling us to get clear about the nature of the relation being considered.
What about the notion that morality might be grounded in grammar? How are we to think of the idea that the wrongness of an action is part of the very concept of the action (is internal to its description)? Would that mean that someone who murders an innocent human being or who lies to a friend is in violation of grammar or in the grip of a grammatical confusion?
Campbell quotes Cora Diamond’s “Eating Meat and Eating People”:
Well, there might be circumstances in which a person would find herself reduced to eating her dog, for instance, to fend off imminent starvation. So perhaps we might reformulate the point as follows: to think of an animal as a pet is not to think of it as food - though the fact that a person will eat something in a dire situation, or, say, as part of a ritual, does not entail that she thinks of it as food.[T]here are some actions. . . that are part of the way we come to understand and indicate our recognition of what kind it is with which we are concerned. [. . .] [I]t is not “morally wrong” to eat our pets; people who ate their pets would not have pets in the same sense of the term. (C. Diamond, The Realistic Spirit, MIT Press, 1991, p. 323.)
Would the realization that if I thought of my dog as food I would not regard it as a pet in the same sense as others do somehow keep me from eating it? Why should it? I might simply shrug my shoulders and say to myself: “All right, so my dog isn’t a pet in that sense.” The fact that we don’t think of pets as food is bound up with the fact that we aren’t tempted to eat them, indeed we normally have a revulsion to eating them. In that sense, not regarding pets as food is not a “mere convention”, notwithstanding the fact that customs concerning what kinds of animal are food vary between cultures. (In China, for instance, the attitude towards eating dog meat is different: there is a movement afoot there to discourage the eating of dogs and cats. In this connection, one may need to distinguish between eating certain species of animals often kept as pets, and eating one’s own pets.)
Now could we imagine people who shared our attitudes to pets in most respects, but regarded them as food? First, we should recall that “our” attitude to pets vary greatly: pets are a varied category (the Swedish category husdjur even more so), and so is the category of pet owner: not every dog owner has his dog sign Christmas cards or brings flowers to his cat’s grave each year on the date of her death. Anyway, if there is a conflict between regarding an animal as food and having towards it the other attitudes that go with regarding an animal as a pet, the conflict is of a psychological kind; a matter of “human nature”. This by itself entails nothing as to the way pets should be treated.
Could we, on the other hand, imagine a society lacking anything corresponding to our concept of a pet? Without difficulty: though of course, life in that society would differ markedly from ours in several respects.