What ancient Greek and Roman philosophers thought about vegetarianism

Writing in a letter to his friend Lucilius around AD62, the Roman philosopher Seneca outlined two arguments for vegetarianism. The first argument came from a Roman philosopher called Sextius whom Seneca particularly admired, who had lived in the first century BC and had been known for his simple lifestyle.

Sextius argued that humans can get all the nutrition we need from eating plants. This means that killing animals for food is done purely for the pleasure derived from eating meat. Sextius believed that killing animals for pleasure makes people develop the habit of cruelty. Morally speaking, people shouldn’t develop the habit of cruelty, so we shouldn’t kill animals just for the pleasure of eating meat.

This argument is different from most modern arguments for vegetarianism, which usually focus on animal rights, arguing that animals deserve care or that killing them causes unnecessary suffering.

The habit of cruelty argument does not focus on the animals at all. Rather it focuses how eating meat affects the people doing the eating. It warns us that by making cruelty a habit, eating meat harms people’s character.

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Even if we theoretically agree that you can get all the nutrition you need from plants and that people morally shouldn’t develop the habit of cruelty, there are still a couple of problems with this argument.

You might ask: “who is developing the habit of cruelty?” Most meat eaters are not doing killing the animals they eat themselves. So, arguably, it’s those doing the killing that are developing cruel habits. Most of us aren’t these people, but likely wouldn’t want anyone to become cruel because of our own pleasure-seeking behaviour either.

All this depends, however, on whether killing animals for meat does in fact develop the habit of cruelty. Certainly, taking pleasure in killing for its own sake could. But most people don’t enjoy killing animals, only eating them.

The transmigration of souls argument

Seneca discusses another argument, which he learned from the biographer Sotion, and which went back to Pythagoras (yes, the one with the theorem).

Pythagoras believed that each soul passed from one body to another after death. He called this “transmigration”. So, when your parent dies, for example, their soul might move into the body of an animal. If you then kill that animal for food, you would have accidentally killed your parent.

You might reply: “Well I don’t believe in the soul” or “I don’t believe that it passes from one body to another”. Sotion has a counter argument. Even if you don’t believe in transmigration, it is still possible that transmigration is true. And if there’s any chance at all that an animal might house the soul of a loved one, that chance alone should be enough to make you avoid eating meat.

Are you persuaded? It is interesting that Sotion argues that you don’t need to accept transmigration to refrain from eating meat. You just need to think that transmigration is possible.

But even if you believe in transmigration, I don’t personally think this argument means you should stop eating meat. Suppose transmigration is true and you kill the animal that happens to have your loved one’s soul. Well, your loved one is fine – their soul simply moves to another body.

Maybe if you think that each soul only gets a limited number of lives, you might worry that by ending the animal’s life you destroy the soul of your parent. But this depends on the version of transmigration you believe in.

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Even if it fails, there is something compelling behind the transmigration argument. The thought behind Pythagoras’ transmigration view is that humans and animals are alike. If a human soul can enter an animal body, humans and animals must be very similar kinds of creature. And if animals really are like us, why are we prepared to kill animals for food, but not other humans?

Vegetarianism wasn’t common in the ancient world. But it did have some adherents, often from religious sects, such as the Pythagoreans. But eating meat was associated with religious observance too and there was a sophisticated debate between philosophers about eating animals.

We know this from Porphry’s book-length defence of ethical vegetarianism On Abstinence from Animal Food (3rd century AD), which is a great place to find out more about ancient arguments for vegetarianism.

Matthew Duncombe receives funding from the Loeb Classical Library Foundation and the British Academy.