Home / F. Edge cases and hypotheticals / Part DIR
"What if they discover that plants feel?"
today there's no evidence that plants feel (A14). But if that were ever discovered, the conclusion wouldn't be "so it makes no difference whether we eat animals". It would be the opposite: the sentience criterion would come to include plants, and the way to cause the least harm would still be to eat plants directly, because animals raised for food eat far more plants than we would. The discovery would increase the number of beings who count; it wouldn't reduce the weight of those who already count.
Short answer
Today there's no evidence that plants feel. But if it were ever discovered, the best way to cause less harm would still be to eat plants, because the animals that become food eat far more plants than we would eat directly. The discovery would increase the number of beings who count; it wouldn't make it acceptable to exploit those we already know feel.
For children
Imagine plants could feel a tiny bit. A little pig needs to eat lots of plants to grow. So if we eat the little pig, all the plants it ate count too. If we eat the plants directly, we use far fewer plants. Even then, eating plants would be the choice that hurts the least.
"If plants did feel, would you choose the diet that kills more plants or the one that kills fewer?"
Como pode aparecer
"What if they discover that plants feel?"
"What will you eat then, rocks?"
"When they prove lettuce screams, let's see the vegans then."
"If everything feels, why not eat meat?"
"If plant sentience is confirmed, the sentience criterion no longer distinguishes between diets."
"Plants feel too." (which is A14)
The strongest version
"What if science discovers tomorrow that plants feel? What will you eat then?"
Strongest version (steelman):
- P1Veganism rests on the sentience criterion: those who feel shouldn't be harmed unnecessarily.
- P2If plants are sentient, eating plants will also harm sentient beings.
- P3Since we have to eat something, it would be impossible to avoid harming sentient beings.
- CSo veganism would lose its point, and eating animals would be no worse than eating plants.
P1 is true. P2 and P3 would be true in this hypothetical scenario. The problem lies in the conclusion: from "we can't avoid all harm" it doesn't follow that "it makes no difference how much harm we cause".
The argument is invalid: the impossibility of reducing harm to zero doesn't make every choice equivalent.
Full answer
- a
Reconstruction and diagnosis
The argument depends on a step that doesn't hold:
Step What it claims Status If plants feel, every diet causes harm True in this scenario Partly true today already: every diet causes some harm (H2) If every diet causes harm, it makes no difference which we choose False Harms can be larger or smaller So eating animals is acceptable Doesn't follow The comparison of quantities still decides - b
Where the argument breaks
1. Today the hypothesis has no basis.
Plant biologists have concluded that plants neither possess nor require consciousness: they have no neurons, no brain and no evolutionary reason for it (A14). Discussing the scenario is useful as an exercise, but it doesn't describe the world as it is.
2. Even in the scenario, eating plants would cause less harm.
About 36% of the calories from the world's crops go to animal feed, and only about 12% of those calories reach people as meat, milk and eggs. Eating animals means consuming, indirectly, far more plants. If plants mattered, eating animals would be the worst of both worlds.
3. Not being able to reach zero harm doesn't license any harm.
We can't prevent every road accident either, and no one concludes that driving carefully or drunk makes no difference. The ethics of taking sentience seriously has always been about reducing harm, not achieving purity (L5).
4. The sentience criterion gets stronger, not weaker.
It follows the evidence: if the evidence showed that plants feel, they would come to count, just as fish, octopuses and crabs came to count as the evidence grew. A criterion that adjusts to the facts is exactly what we should expect from an honest ethics.
5. There would be degrees to consider.
If plants had some form of experience, we'd need to estimate its probability and intensity, as we do with insects (A15). That would call for proportionate caution, not indifference.
6. The human test.
When it was recognized that more groups of people were capable of suffering than had been admitted, the right conclusion was to extend consideration to them, not to conclude that no one's suffering matters.
- c
Data and sources
Source What it says Note Taiz et al., 2019 Plants neither possess nor require consciousness Trends in Plant Science, 24(8) Cassidy et al., 2013 36% of the calories from the world's crops become animal feed, and only 12% of those calories reach human diets Environmental Research Letters, 8(3) *A Journey Through Animal Ethics*, vol. VI, ch. 21 If plants were morally considerable, eating animals would still be worse Basis for point 2 Birch, The Edge of Sentience (2024) Proposes precautions proportionate to the evidence of sentience Oxford University Press - d
The strongest counter-reply: veganism would lose its clarity
The most serious version says: veganism's appeal is the clear line between those who feel and those who don't. If plants felt, that line would vanish, and veganism would become a complicated calculation of quantities, without the moral force it has today.
- e
Why the counter-reply doesn't reach the conclusion
Clarity was never the foundation.
The foundation is not causing unnecessary harm to those who feel. If the line moved, the obligation would remain, just applied to more beings.
The calculation already exists today.
The calculation would still favor plants.
Even in the most complicated scenario, eating plants directly would cause less harm than eating those who ate them.
Reasoning errors
Logical
Is the form valid?
Nirvana fallacy
False equivalence
Epistemological
Does the evidence support it?
Hypothesis treated as fact
Moral
Is the criterion coherent?
Ignoring quantities
Biases
Motivated reasoning
A hypothetical scenario is used to dismiss change in the present
General literature on motivated cognition
The meat paradox
Diluting the criterion eases the tension between liking animals and eating them
Extrapolations
The principle being tested is: "if all harm can't be avoided, it makes no difference how much harm we cause".
If it applied to…DrivingTap to see
It would make no difference whether you drive carefully or drunk, because accidents happen
No one accepts this
If it applied to…MedicineTap to see
It would make no difference whether a treatment has more or fewer side effects
Absurd
If it applied to…FoodTap to see
It would make no difference whether we eat plants or those who ate many plants
This is the argument's conclusion
Contradictions
No one concludes it makes no difference whether you drive carefully because accidents happen.
If plants mattered, the concern would lead to eating plants directly.
The scenario is used only against veganism.
What the argument gets right
What is true
It's right that ethics has to stay open to evidence: if it were ever discovered that plants feel, that would have to be taken seriously, and anyone who holds the sentience criterion couldn't ignore it. It's also right that no diet is free of causing some harm.
But
But the discovery wouldn't make everything equivalent. The way to cause the least harm would still be to eat plants, not animals fed on large quantities of them.
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:
- If Plants Are Morally Considerable, Does It Make No… Vol. VI, ch. 21
- What About Plants? Vol. IV, ch. 4
References
Science
- Plants neither possess nor require consciousness. *Trends in Plant Science*, 24(8).
- Redefining agricultural yields: from tonnes to people nourished per hectare. *Environmental Research Letters*, 8(3).
Philosophy
- The Edge of Sentience. Oxford University Press.
- If plants are morally considerable, does it make no difference whether we eat animals or plants? In *A Journey Through Animal Ethics*, vol. VI.