Naturalistic Fallacy
Moore’s naturalistic fallacy concerns identifying goodness with a natural property, such as pleasure. Related but distinct problems are deriving an ought from purely descriptive premises and assuming that whatever is natural must be good. Arguments about nature need their ethical premises made explicit.
THE IDEA
39 Naturalistic Fallacy
Three related ideas are often grouped under the naturalistic fallacy. The is–ought problem concerns deriving a normative conclusion from purely descriptive premises. An appeal to nature assumes that something is good or right because it is natural. Moore’s original objection is narrower: it concerns identifying goodness with a natural property. These arguments raise different questions, even when they overlap.
The term originates with G. E. Moore, who used it more narrowly within metaethics. For Moore, “good” is a non‑natural property—logically and metaphysically distinct from any natural property (such as pleasure, evolutionary success, or human function). Any attempt to define good in terms of a natural property commits the naturalistic fallacy, because it confuses a natural object with the entirely different kind of thing that is “good.” Moore famously pointed to John Stuart Mill’s move from the descriptive claim that humans desire happiness to the normative conclusion that happiness is desirable (i.e., good) as a prime example: purely natural, psychological facts are made to yield a substantive moral claim without justification.
The fallacy also appears frequently in everyday reasoning. For instance:
- “Homosexuality is unnatural (because animals do not engage in it), therefore it is immoral.”
- “It is natural for humans to be selfish, so we ought to be selfish.”
In these cases, a factual claim about nature—often itself questionable—is used as the only grounds for a moral “ought.” The problem is not just the questionable factual premise; it is the leap from a description to a prescription without any intervening ethical framework. A related reverse error is the moralistic fallacy: inferring what is the case from what one thinks ought to be the case.
However, not every move from natural facts to normative conclusions is universally regarded as fallacious. Moore’s objection rests on his view that goodness is not identical to a natural property. This does not mean that natural objects cannot be good. Ethical naturalists dispute his account of goodness, but that dispute does not make an inference from purely descriptive premises valid without further premises. Aristotle’s function argument, for example, moves from the natural function of a flute‑player (or a human being) to what is good for that being. On Aristotle’s view, the function of a thing is already imbued with normative content—the good of a flute‑player is to play the flute well. Similarly, Thomas Aquinas’s natural law theory holds that fundamental natural facts about humans (preservation of life, rearing of young, social living) are not merely descriptive; they are intrinsically normative because they follow from our nature and our end. In such frameworks, certain “natural” facts are already value‑laden, so reasoning from them to normative conclusions is not a logical defect.
These views disagree about the nature of value and about which premises already contain normative commitments. An argument must explain how it gets from an “is” to an “ought.” Ask what ethical premise connects the stated fact to the proposed duty, and whether that premise is defensible. A framework that treats human functions as value-laden is doing more than drawing a conclusion from a bare description.
When to use it
In debates about sexual orientation, opponents may argue that homosexuality is unnatural and therefore immoral. Recognizing the fallacy helps to separate factual claims from moral ones.
In discussions about diet, distinguishing evidence about health effects from the assumption that ancestral or natural practices must be better.
In environmental ethics, examining the ethical premise that makes a landscape’s naturalness a reason to preserve it.
In conversations about gender roles, arguments that traditional roles are 'natural' and therefore correct are examples of the naturalistic fallacy.
Evaluating arguments in political debates that claim because something is 'natural', it is 'good' (e.g., 'Humans are naturally competitive, so capitalism is good').
Assessing scientific or policy arguments that derive moral obligations from biological or psychological facts.
Analyzing religious moral arguments that derive 'ought' from divine nature.
Critical thinking in ethics papers: identify when a writer mistakenly equates a descriptive property with a normative property.
FROM THEORY TO EVERYDAY LIFE
In practice
Homosexuality is unnatural
An argument labels homosexual behavior unnatural and concludes that it is immoral. Even if its factual description were accurate, the moral conclusion would require a premise connecting naturalness with moral worth. That premise needs its own defense.
Selfishness is natural
A claim that since humans are naturally selfish, we ought to act selfishly. This ignores that we routinely go against natural impulses for moral reasons, and nature itself is not a reliable moral guide.
Mill's Hedonistic Argument
Moore criticizes the move from the observation that people desire happiness to the conclusion that happiness is desirable in the moral sense. His objection is that the descriptive observation does not by itself establish what ought to be desired.
Aristotle's Function Argument
Aristotle argues that a thing's function determines its good, e.g., a flute-player's good is playing well. This appears to derive normative value from a natural/descriptive property (function), but Aristotle's metaphysics entwines natural and normative.
Aquinas's Natural Law
Aquinas connects human inclinations, such as preserving life and living socially, with human goods. His natural-law framework gives those inclinations normative significance; it is not simply an inference from a description with no ethical premise.
A MOMENT TO REFLECT
Put it to work.
Can you recall a time you assumed that because something is common or natural, it must be right? How would you challenge that assumption?
What ethical premise would connect a description of nature to a moral duty? Identify an argument in which that premise is left unstated.
In what political or ethical debates is the naturalistic fallacy frequently used? How would you refute it?
Can you think of an argument that moves from descriptive facts to moral conclusions? Does it commit the naturalistic fallacy according to Moore?
How might one's metaethical commitments affect whether an inference from 'is' to 'ought' is considered fallacious?
Consider Aristotle's function argument: does it rely on a valid inference or is it a naturalistic fallacy? Why?
Often confused with
References
- Principia Ethica — G.E. Moore (2009)
- Nicomachean Ethics — Aristotle (2009)
- Summa Theologica — Thomas Aquinas (1997)
CONTINUE THE CONVERSATION
Source texts
- Bad Arguments 100 of the Most Important Fallacies in Western Philosophy (Steven Barbone, Michael Bruce)
- Logically Fallacious - The Ultimate Collection of Over 300 Logical Fallacies