Home / F. Edge cases and hypotheticals / Part DIR
"Oysters and mussels don't feel."
the argument is partly plausible, and that is exactly why it confirms the criterion. Oysters and mussels have very simple nervous systems, with no centralized brain, and some philosophers who defend animals admit they may not feel. But by saying "they don't feel, so it's fine", the person accepts that what matters is sentience. And that criterion condemns eating every animal who does feel, including fish, octopuses and crabs.
Short answer
You may be right about oysters and mussels: they have very simple nervous systems, and even some animal advocates admit they may not feel. But by saying that, you accept that what matters is whether the animal feels. And that criterion condemns eating fish, octopuses, crabs, chickens and pigs, who do feel. The exception, if it exists, proves the rule.
For children
Some animals, like oysters and mussels, are very simple and may not feel pain. Scientists are still studying this. But if we decide that only those who feel matter, then we need to look after everyone who does feel, like fish, octopuses, chickens and pigs.
"If what matters is whether the animal feels, why eat the ones who do?"
Como pode aparecer
"Oysters and mussels don't feel."
"Oysters have no central nervous system."
"Bivalves are almost plants."
"A vegan who won't eat oysters doesn't understand biology."
"Bivalves are probably not sentient."
"Fish and invertebrates don't feel pain." (which is A6)
The strongest version
"Oysters have no central nervous system. Bivalves are almost plants."
Strongest version (steelman):
- P1Oysters and mussels have no centralized brain and have very simple nervous systems.
- P2Without that kind of system, they're unlikely to be sentient.
- P3If they aren't sentient, eating them causes no suffering.
- CSo eating oysters and mussels is acceptable.
P1 is true. P2 is plausible, but uncertain. P3 is true if P2 is. The most important point is that the argument accepts sentience as the criterion.
The argument is valid and perhaps sound for bivalves. But it can't be used to defend eating animals who feel, and the uncertainty about P2 is a reason for caution.
Full answer
- a
Reconstruction and diagnosis
The argument accepts the sentience criterion, and that has consequences:
Animal Evidence of sentience What the criterion implies Mammals and birds Strong Don't eat Fish Strong and growing Don't eat Octopuses and crabs Strong, recognized even in UK law Don't eat Oysters and mussels Weak and uncertain Perhaps acceptable; caution advised - b
Where the argument breaks
1. It confirms the criterion.
If the problem is the lack of sentience, sentience is what matters. That's exactly the criterion of veganism and animal ethics.
2. The exception doesn't extend.
Octopuses, squid, crabs and lobsters show strong evidence of sentience. In 2021, a London School of Economics report recommended treating them as sentient, and the United Kingdom included them in its animal sentience law in 2022.
3. Uncertainty calls for caution.
Bivalves have nerve ganglia and react to stimuli. The absence of strong evidence isn't strong evidence of absence. When in doubt, the cost of not eating them is very small.
4. The exception doesn't cover the rest of the plate.
Some people eat only bivalves for this reason, but most of the time the argument comes from people who eat many other animals, for whom it doesn't hold.
5. Harvesting and farming bivalves also have effects.
Collection and production can affect other animals and ecosystems, which should be taken into account.
- c
Data and sources
Source What it says Note Birch et al., LSE, 2021 Reviewed over 300 studies and recommended treating cephalopods and decapod crustaceans as sentient Doesn't cover bivalves United Kingdom, Animal Welfare (Sentience) Act 2022 Includes cephalopods and decapod crustaceans among sentient animals British law The New York Declaration on Animal Consciousness (2024) Recognizes a realistic possibility of consciousness in many invertebrates Signed by hundreds of researchers - d
The strongest counter-reply: veganism should then accept bivalves
The most serious version says that if bivalves probably don't feel, veganism should accept them, and that refusing them shows the movement is dogmatic.
- e
Why the counter-reply doesn't reach the conclusion
Some animal advocates do accept them.
Some philosophers and activists consider eating bivalves acceptable. The debate is honest and open.
Caution isn't dogma.
Faced with uncertainty, preferring not to take the risk is a reasonable position.
Nothing changes for the other animals.
Accepting bivalves or not doesn't affect the conclusion about animals who feel.
Reasoning errors
Logical
Is the form valid?
Fallacy of accident (converse)
Epistemological
Does the evidence support it?
Absence of evidence taken as evidence of absence
Moral
Is the criterion coherent?
Criterion used only where convenient
Biases
Motivated reasoning
The favorable case is remembered; the unfavorable ones, forgotten
General literature on motivated cognition
Extrapolations
The principle being tested is: "if an animal doesn't feel, eating it isn't wrong".
If it applied to…Oysters and musselsTap to see
Perhaps acceptable
With caution because of the uncertainty
If it applied to…Octopuses and crabsTap to see
Not acceptable, because they feel
Recognized in UK law
If it applied to…Fish, birds and mammalsTap to see
Not acceptable, because they feel
The principle condemns almost all consumption
Contradictions
And eats clearly sentient animals.
The argument doesn't describe their own consumption.
In medicine, safety, the environment.
What the argument gets right
What is true
The argument is largely right. Bivalves are genuinely hard cases, the science about them is uncertain, and some animal advocates admit they may not feel. Recognizing this is a sign of honesty and shows that veganism rests on criteria, not dogma.
But
And it's precisely that criterion that settles the rest. Whoever accepts that what matters is feeling already has the answer for every other animal on the plate.
Connections
Usually comes before
Usually comes after
Go deeper in Questão de Ética
Chapters from the open-access collection A Journey Through Animal Ethics that discuss this argument in more detail:
- Uncertainty About Sentience and the Benefit of the Doubt Vol. II, ch. 13