Appeal to nature

“It’s all natural, so it’s safe”

A gardener recommends a pest spray made from plant extracts: “It’s all natural, so you don’t have to worry about using it around the vegetables or the dog.”

Whether a spray is safe depends on what’s in it and how much, not on whether it came from a plant. Plants make many compounds precisely because they’re toxic to the things that eat them. Nicotine, from tobacco, was long used as an insecticide and is toxic to people too. The spray may well be fine, but “natural” hasn’t shown it.

“Unnatural” as the whole objection

“I won’t buy lettuce grown indoors under LED lights. Food should come from soil and sunlight. It just isn’t natural.”

“Unnatural” describes how the lettuce was grown. It doesn’t say what’s wrong with it. The real questions (taste, nutrition, price, energy use, pesticides) each have answers that can be checked, and they might favor either lettuce. The line is also hard to draw: field lettuce is itself a domesticated plant, usually irrigated and fertilized, so the objection is really to one kind of human intervention and not another.

“It’s only natural”

“Everyone procrastinates. It’s human nature. So there’s no point trying to fight it.”

Here “natural” means common or instinctive, which is the version that sounds most reasonable. And part of it is relevant: a tendency almost everyone shares is probably hard to change, and a good plan should expect it. But “most people do this” doesn’t show that it’s good, or that it can’t be managed. Plenty of common tendencies (forgetting, impatience) are things people reasonably work to counter.

Spelled out, the argument needs a premise it rarely says aloud:

The step from premises to conclusion is fine. The problem is the unstated premise, and it fails differently depending on what “natural” means. John Stuart Mill, in his essay “Nature”, separated the two main senses:

• Everything that exists and happens by natural laws. In this sense, human inventions are natural too, since people can only act through natural forces. “Natural things are good” then applies to everything, so it can’t favor anything. Mill called the advice to follow nature, in this sense, “unmeaning”.
• What happens without human intervention. In this sense the premise is simply false. Nature without people includes disease, drought and predators, and nearly all useful human activity consists of changing it. Mill called following nature in this sense “irrational and immoral”.

Arguments from nature often borrow the plausibility of one sense and the force of the other. That slide between meanings is equivocation: the same word used in two senses within one argument.

It isn’t the same as the naturalistic fallacy, though the two are often confused and they do overlap. G. E. Moore coined “naturalistic fallacy” in Principia Ethica (1903) for a claim about definitions: the mistake, as he saw it, of treating “good” as meaning the same as some other property, such as “pleasant” or “more evolved”. His target wasn’t the word “natural” in the everyday sense; he gave the same name to defining “good” in terms of a supposed reality beyond the senses. Moore did discuss arguments for living “according to nature”, and concluded that arguing a thing is good because it’s natural is fallacious, as one instance of his broader error. But the two come apart. Someone can commit Moore’s fallacy without mentioning nature (“good just means pleasant”), and most everyday appeals to nature (“it’s natural, so it’s safe”) make no claim about what “good” means. Whether Moore’s own argument succeeds is still debated, and commentators note that the name is misleading: even if Moore identified a real mistake, it isn’t a fallacy in the logical sense.

It isn’t the same as the is–ought gap either. David Hume, in A Treatise of Human Nature (1739–40), noticed that writers on morality often slip from statements about what is to conclusions about what ought to be, without explaining how one follows from the other. An appeal to nature in ethics (“it’s natural, so we ought to do it”) is one way to make that slip, but the gap is wider than naturalness: any purely factual premise faces it. And many appeals to nature are about safety or health, which are factual claims with no “ought” in them at all.

• Natural, so good: the positive form. “It’s plant-based, so it can’t hurt you.”
• Unnatural, so bad: the negative form, often carrying unease or disgust. “Lab-grown diamonds are unnatural, so they must be inferior.” (They’re the same material as mined diamonds.)
• Human nature: “natural” meaning common or instinctive. “It’s natural to be jealous, so there’s nothing wrong with acting on it.”
• “Everything is natural”: the broad sense, used to wave a concern away. “Plastic is made from oil, and oil is natural.” This stretches the word until it covers everything, which also leaves it saying nothing.

“Natural” does legitimate work when it stands for something more specific that can be checked.

• Shorthand for a specific, relevant property. “No added sulfites” matters to someone with a known sensitivity to sulfites. The reason is the absent ingredient, not naturalness, and it holds only as far as the ingredient is actually absent.
• A track record is the actual evidence. A plant that has grown in a region for thousands of years without watering is evidence that it can survive the local rainfall. That’s evidence about a particular outcome, observed over time, not a claim that natural is better in general.
• Shorthand for a documented effect. Saying a river’s “unnatural” straightened channel causes flooding downstream is fine if the flooding is what’s being measured and cited. The word labels the cause; the evidence carries the argument.
• Plain description. “A natural lake” just means no one dug it. Nothing evaluative follows, and nothing is being argued.
• Preference, stated as preference. Liking the look of natural wood, or simply preferring food with a short ingredient list, isn’t an argument. It becomes one only when the preference is presented as proof that the thing is better.

The test: take out the word “natural”. Is there still a reason?

Native plants for a dry garden

“Plant native grasses instead of a lawn. They’ve grown here for thousands of years on local rainfall alone, so once they’re established they’ll likely need far less watering.”

This sounds like “native, so better”, but the argument doesn’t rest on naturalness. It rests on a long track record about the specific thing being predicted (surviving this climate’s rainfall), and the conclusion is limited to that. It doesn’t claim native grasses are better in every way, or better looking.

A fragrance-free product for a known reaction

“My dermatologist’s patch test showed I react to a fragrance ingredient, so I buy fragrance-free soap. A ‘natural’ fragrance could still contain the same ingredient.”

The choice looks like a preference for the plainer, more “natural” product, but the reason is a specific, relevant property confirmed by a test. The speaker even rejects the appeal to nature: a plant-derived fragrance isn’t assumed to be safe.

The preference for natural things is strong and well documented. In surveys of American students and adults, Paul Rozin and colleagues (2004) found that people preferred natural to artificial options, more for foods than for medicines. When the natural and artificial versions were described as equally healthy or effective, most people who preferred natural still did, and when the two were described as chemically identical, a majority still did. The authors suggest that a substantial part of the preference is ideational (moral or aesthetic) rather than instrumental (about health, effectiveness or taste). That’s what makes the appeal persuasive: it draws on a value people already hold, which can feel like evidence.

Rozin (2005) also found that people judge naturalness mostly by how something was processed rather than by what it contains. Adding a gene from another species lowered perceived naturalness the most, while domestication, which also changes plants and animals in major ways, was seen as much less damaging. So “natural” tracks a story about a thing’s history, which is not the same as its safety or value.

The appeal also borrows from a reasonable habit. Some things people have used for a long time have been tested by that use, and some processed things are worse. The mistake is to turn that loose tendency into a rule. Like the Appeal to popularity and Chronological snobbery, it substitutes a feature of an idea or a product (how popular it is, when it arose, where it came from) for evidence about whether it’s any good.