A Snippet of Dialogue

Arthur: Sentience—the capacity to suffer—marks the limit of moral considerability. If a being is sentient, its suffering must be taken into account in our deliberations. Nonsentient beings such as rocks and plants have no interests, so there is nothing to be taken into account.

Betty: What about insects and oysters? Are they sentient?

Arthur: If they are, their suffering must be taken into account. If not, not.

Betty: But are they sentient?

Arthur: That’s a factual question about which reasonable people can differ. Don’t confuse the category with its members. Just because it’s not clear whether a particular being goes in the sentient category doesn’t mean (1) that the category itself is unclear or (2) that there is no difference, after all, between being sentient and being nonsentient. Compare baldness. Everyone, logically speaking, is either bald or nonbald, but there are individuals who are not easily classified. That there are hard cases doesn’t entail that there are no easy cases. That a concept is not perfectly clear doesn’t entail that it’s perfectly unclear. Some people are clearly bald. Some people are clearly nonbald. Some people are neither clearly bald nor clearly nonbald.

Betty: But how can you use a category or concept—sentience—if it doesn’t allow all individuals to be easily classified?

Arthur: Easily. The animals we use as mere means to our ends—cows, pigs, chickens, turkeys, rats, monkeys—are clearly sentient. They’re not borderline cases. Why should the fact that there are other animals of doubtful sentience, such as oysters or insects, obscure this fact from us? Is a concept useful only if it is perfectly clear, i.e., only if it has no degree of vagueness? Most ordinary concepts are vague to some extent, but they remain useful to us. The concept of an automobile is useful, but there are hard cases of automobiles where we’re not sure whether to say, “Yes, it’s an automobile” or “No, it’s not an automobile.”

Betty: My head hurts. Good night.

Arthur: Good night.