Home / A. Sentience and moral status / Part DIR
"Where do you draw the line? Insects? Bacteria?"
the difficulty of drawing an exact line doesn't erase the clear cases. We don't know exactly when day turns into night, and yet noon isn't midnight. Cows, pigs and chickens are clearly on the side of those who feel, and the evidence for fish is strong. In borderline cases, such as insects, the answer isn't to give up: it's to act with precaution proportional to the uncertainty.
Short answer
Not knowing exactly where the line falls doesn't mean there's no difference. We don't know the exact moment someone becomes old, and yet a baby isn't an old person. Cows, pigs and chickens are clearly on the side of those who feel, and the evidence for fish is strong; the real doubts are in cases like insects. And in doubtful cases, the sensible answer is caution, not pretending there's nothing there.
For children
When the day is ending, it's hard to say the exact minute it became night. But no one mixes up noon and midnight. It's similar with animals: it's hard to know if an ant feels, but it's easy to know that a dog, a cow and a pig feel. Not knowing everything doesn't mean we know nothing.
"Since we don't know exactly where childhood ends, is there no difference between a baby and an adult?"
Como pode aparecer
"What about the ants you step on?"
"What about the bacteria you kill washing your hands?"
"If everything matters, nothing matters."
"Vegans kill mosquitoes and still lecture everyone." (which is F9)
"Do shrimp count? Earthworms? Viruses?"
"There's no non-arbitrary boundary between beings that count and beings that don't."
"Gradual criteria don't allow binary decisions."
"Everyone draws the line where they like." (which leads to E2)
The strongest version
"If animals matter, what about ants? And the bacteria you kill washing your hands? Where do you draw the line?"
Strongest version (steelman):
- P1A moral criterion is only acceptable if it lets us draw a clear line between those who count and those who don't.
- P2Sentience doesn't let us draw that line: it's gradual and uncertain in borderline cases.
- C1So sentience isn't an acceptable moral criterion.
- C2Without a clear criterion, there's no basis for condemning the use of animals.
P2 is partly true: there's real uncertainty about insects and other invertebrates. The problem lies in P1, which demands of a moral criterion a precision no criterion has.
The argument is valid. Its soundness fails at P1. It's the so-called continuum fallacy, or line-drawing fallacy: concluding that if there's no exact boundary, there's no difference.
Full answer
- a
Reconstruction and diagnosis
The argument starts from a truth, that there are hard cases, and draws from it a conclusion about the easy cases.
Being Evidence of sentience Situation Mammals and birds Strong Clear case Fish, cephalopods, decapod crustaceans Strong or realistic Clear or nearly clear case (A6) Insects Realistic possibility, with uncertainty Borderline case Plants Practically none Clear case on the other side (A14) Bacteria None Clear case on the other side The animals farming exploits most are in the first two rows. The uncertainty of the middle rows changes nothing about them.
- b
Where the argument breaks
1. A fuzzy boundary doesn't erase clear cases.
Almost every important concept has fuzzy boundaries: childhood, baldness, wealth. That has never stopped anyone from telling a child from an adult. Demanding an exact line from a moral criterion is demanding something no criterion offers.
2. Science already distinguishes clear cases.
The 2024 New York Declaration on Animal Consciousness stated that there is strong evidence of conscious experience in mammals and birds, and a realistic possibility in all vertebrates and in many invertebrates, including cephalopods, decapods and insects.
3. Uncertainty has a method.
The philosopher Jonathan Birch proposes treating beings with sufficient evidence as "sentience candidates" and adopting proportionate precautions. The question stops being "does it feel or not?" and becomes "how likely is it, and how large is the harm at stake?".
4. Bacteria and insects aren't the case of farming.
5. "If everything matters, nothing matters" doesn't follow.
That many beings matter to some degree doesn't make them all matter equally or cancel the differences. The right conclusion is to weigh, not to give up.
- c
Data and sources
Source What it says Note New York Declaration on Animal Consciousness (2024) Strong evidence in mammals and birds; a realistic possibility in all vertebrates and in many invertebrates, including insects; certainty shouldn't be required before considering welfare risks Signed by scientists and philosophers Birch, The Edge of Sentience (2024) Proposes the concept of a sentience candidate and precautions proportionate to the evidence Oxford University Press; checked against reviews and summaries Taiz et al., 2019 Plants neither possess nor require consciousness Used for the clear side of the line - d
The strongest counter-reply: the line decides who eats what
The most serious version says that, in practice, some line has to be drawn to decide what may be eaten, and that any line, whether at vertebrates, insects or bivalves, will be partly arbitrary. If vegans also draw an arbitrary line somewhere, why would theirs be better than that of someone who draws it at the human species?
- e
Why the counter-reply doesn't reach the conclusion
Not every line is equally arbitrary.
A line that follows the evidence of sentience, even with a margin of error, is far less arbitrary than a line at the species, which leaves out beings who clearly feel (A10).
Erring on the side of caution is better than erring on the side of disregard.
If the line has to have a margin, the margin should protect those who may feel, not expose those who certainly do.
Doubt about borderline cases doesn't protect farming.
Cows, pigs and chickens aren't on the borderline.
Veganism already deals with this.
It seeks to avoid harm "as far as is possible and practicable", without demanding certainty about every being (L4).
Reasoning errors
Logical
Is the form valid?
Continuum fallacy
Changing the question
Epistemological
Does the evidence support it?
Selective demand for certainty
Moral
Is the criterion coherent?
False dilemma
Biases
Motivated reasoning
The difficulty of the boundary is used to dismiss the clear cases
General literature on motivated cognition
Scope insensitivity
Billions of clearly sentient animals get diluted in a discussion about bacteria
Linked to K1
In-group bias
The only line accepted without discussion is the species line
Extrapolations
The principle being tested is: "if there's no exact line, there's no difference".
If it applied to…AgeTap to see
There'd be no difference between a baby and an adult
No one accepts this
If it applied to…Day and nightTap to see
Noon and midnight would be the same
Absurd
If it applied to…Criminal lawTap to see
There'd be no way to tell a minor from an adult
The law uses approximate lines without denying differences
If it applied to…PeopleTap to see
There'd be no moral difference between hurting a person and crushing a bacterium
Shows the principle isn't taken seriously
Contradictions
The same person knows the difference between a child and an adult without needing the exact minute.
Uncertainty about ants doesn't make them doubt that the dog feels.
Demands an exact line from vegans and accepts one that excludes those who clearly feel.
That already presupposes knowing which side of the line animals are on.
What the argument gets right
What is true
The question is a good one. There's real uncertainty about the sentience of insects and other invertebrates, and that uncertainty has enormous practical consequences, given how many of these animals there are. It's also true that any moral criterion requires some degree of judgment in borderline cases.
But
But the existence of hard cases doesn't make the easy cases hard. The right response to uncertainty is proportionate precaution, not indifference. And farming doesn't exploit borderline beings: it exploits cows, pigs, chickens and fish, about whom the doubt is minimal.
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:
- Does the criterion of sentience exclude insects? Vol. VI, ch. 6
- Uncertainty About Sentience and the Benefit of the Doubt Vol. II, ch. 13
References
Science
- The New York Declaration on Animal Consciousness.
- Plants neither possess nor require consciousness. *Trends in Plant Science*, 24(8).
Philosophy
- The Edge of Sentience: Risk and Precaution in Humans, Other Animals, and AI. Oxford University Press.