Philosophy 142 - 8.1.2 The Naturalistic Fallacy

When thinking about values, it can be easy to make errors. A fallacy is an error in logical reasoning. Fallacies involve drawing the wrong conclusions from the premises of an argument or jumping to a conclusion without sufficient evidence. There are many types of logical fallacies because there are many ways people can make mistakes with their reasoning.


Learn more about informal fallacies in the chapter on logic and reasoning, and explore more about cognitive values in the chapter on critical thinking, research, reading, and writing.

The naturalistic fallacy is an error in reasoning that assumes you can derive values (what people ought to do) from facts about the world (what is the case). The British philosopher G. E. Moore (1873–1958) explains the problem with this fallacy in his 1903 book Principia Ethica. For Moore, if philosophers based the judgment “x is good” on a set of facts, or natural properties, about x, they have committed the naturalistic fallacy.

There are frequent examples of the naturalistic fallacy in popular discourse. Debates about whether monogamy is good or bad are frequently posed in terms of whether it is “natural,” and proponents for either side of the argument often point at monogamous or nonmonogamous animals to justify their answer. Claiming what humans ought to do from observations about animal behavior is an attempt to derive values from facts about the world.

Hume and the Is-Ought Problem

The naturalistic fallacy is related to the is-ought problem. This problem asserts the challenge of moving from statements of fact (something is) to statements of value (something ought to be). The Scottish Enlightenment philosopher David Hume (1711–1776) provides one of the most famous explanations of this problem in his A Treatise of Human Nature (1739–1740).

A lounging domestic cat looks directly at the viewer.
Figure 8.2 The descriptive claim “Having pets has been shown to improve people’s mental health” can easily become the evaluative claim “People ought to have pets.” This is known as the is-ought problem. (credit: “My cat Toby” by Richard J/Flickr, Public Domain)

At the time Hume was writing the Treatise, philosophers were rejecting a morality based on religious faith or dogmatic beliefs and were instead trying to find justifications for morality that relied on undeniable reasons for being a good person or trying to build a better society. Hume countered that you cannot derive ought from is because morality has to do with sentiments, not facts. In other words, morality has to do with what people believe and how we feel, and beliefs and feelings are not factual or derivable from facts. As Hume explains in the passage below, facts have to do with relations between objects. Morality, however, has to do with a human subject expressing their sentiments about a matter.

Read Like a Philosopher

Read this excerpt from David Hume’s ATreatise of Human Nature, Book 3, Part 1. As you read, pay attention to how he describes propositions that use “ought.” Does he seem to think they are justified with proper reasoning? Why or why not? Think of an example where using “ought” statements without rational justification could be a problem.

“I cannot forbear adding to these reasonings an observation, which may, perhaps, be found of some importance. In every system of morality, which I have hitherto met with, I have always remarked, that the author proceeds for some time in the ordinary way of reasoning, and establishes the being of a God, or makes observations concerning human affairs; when of a sudden I am surprized to find, that instead of the usual copulations of propositions, is, and is not, I meet with no proposition that is not connected with an ought, or an ought not. This change is imperceptible; but is, however, of the last consequence. For as this ought, or ought not, expresses some new relation or affirmation, it is necessary that it should be observed and explained; and at the same time that a reason should be given, for what seems altogether inconceivable, how this new relation can be a deduction from others, which are entirely different from it. But as authors do not commonly use this precaution, I shall presume to recommend it to the readers; and am persuaded, that this small attention would subvert all the vulgar systems of morality, and let us see, that the distinction of vice and virtue is not founded merely on the relations of objects, nor is perceived by reason.”

(Source: Hume, David. (1739–1740) 2002. ATreatise of Human Nature, Book III, Part I, Section I. Project Gutenberg. - link2H_4_0085)

The Open-Question Argument

Hume’s description of the is-ought problem lives on in contemporary philosophy, especially in 20th-century ethics. In his 1903 book Principia Ethica, G. E. Moore introduces the open-question argument to argue against the naturalistic fallacy, which he sees as trying to derive non-natural properties, such as “right” and “good,” from natural properties. Unlike claims in the natural sciences, which extend understanding of or express a discovery about natural properties of the world, goodness and rightness are non-natural properties that cannot establish their truth based on natural properties and thus are always open to questioning. For example, the natural properties of water (H20) are not open to questioning in the same way that the non-natural properties of things that people judge to be “good” or “right” are.

In order to answer the question “Is x good?” people frequently have to assert that something else is good. Is being kind to your neighbor good? Yes. Why? Because compassion for others is good. This does not “close” the question because it amounts to saying “good is good.” It is circular and thus uninformative, so the question remains open. Moore did believe that claims about moral properties can be true, but not in the same way as claims about natural properties.

Read Like a Philosopher

Search social media platforms for examples of “is” presented as “ought” statements. What types of beliefs do you notice people presenting as facts? What types of justifications are given for these claims?

The content of this course has been taken from the free Philosophy textbook by Openstax