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Moralistic Fallacy

(also known as: moral fallacy)

Description: When the conclusion expresses what is, based only on what one believes ought to be, or what isn’t is based on what one believes ought not to be.

This is the opposite of the naturalistic fallacy.

In his 1957 paper, Edward C. Moore defined the moralistic fallacy as the assertion that moral judgments are of a different order from factual judgements. Over the years, this concept has been simplified to deriving an “is” from an “ought.”

Logical Forms:

X ought to be.
Therefore, X is.

X ought not to be.

Therefore, X is not.

Example #1:

Adultery, as well as philandering, is wrong.

Therefore, we have no biological tendency for multiple sex partners.

Explanation: While, morally speaking, adultery and philandering may be wrong, this has no bearing on the biological aspect of the desire or need. In other words, what we shouldn’t do (according to moral norms), is not necessarily the same as what we are biologically influenced to do. Also note that moral judgments are more commonly stated as facts (e.g., “philandering is wrong”) than expressed as “oughts” (e.g., “philandering ought to be wrong”). This causes people to confuse the naturalistic and moralistic fallacies.

Example #2:

Being mean to others is wrong.

Therefore, it cannot possibly be part of our nature.

Explanation: While, morally speaking, being mean to others may be wrong, this has no bearing on the biological aspect of the desire or need. Again, what we shouldn’t do (according to moral norms), is not necessarily the same as what we are biologically influenced to do.

Exception: An argument can certainly be made that an ought is the same as an is, but it just cannot be assumed.

Note: The naturalistic and the moralistic fallacies are often confused with the appeal to nature fallacy. One reason, perhaps, is because what is “natural” is another way of saying what is, is. But with the naturalistic and the moralistic fallacies, the conclusion does not have to be based on what is “natural;” it just has to be based on what is. For example,

Men and women ought to be equal. Therefore, women are just as strong as men and men are just as empathetic as women.

This is another example of the moralistic fallacy but not an appeal to nature.


Moore, E. C. (1957). The Moralistic Fallacy. The Journal of Philosophy, 54(2), 29–42.
Pinker, S. (2003). The Blank Slate: The Modern Denial of Human Nature. Penguin.

Registered User Comments

Tuesday, September 20, 2016 - 09:46:37 AM
Your first example is wrong. We do have a biological (and therefore natural) need to pair bond. Oxytocin bonding proves we are biologically monogamous.

Obviously the moralistic fallacy still exists, but the adultery example is poor.

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Bo Bennett, PhD
Tuesday, September 20, 2016 - 10:03:40 AM
Hi Alex, remember that fallacies are not about what is true or not; it is about the form of the argument. Example #1 is still fallacious, therefore correct (correct in the sense that is demonstrates the fallacy). It does not matter what conclusions are reached. Anything that fits the "X is morally wrong, therefore X is unnatural" is fallacious. The conclusions I use in my examples are mostly all wrong anyways, thus the problems with fallacies.

As for your statement "Oxytocin bonding proves we are biologically monogamous," speaking as a social psychologist, that statement is problematic. First, at most, ocytocin is evidence for biological monogamy, certainly not proof of. Second, when biologists use the term "monogamy," that doesn't exclude multiple sex partners. For example, from one study

The term “monogamy” does not imply lifelong exclusive mating with a single individual. In fact, many birds form pair bonds over a season, raise their offspring together, and then select another partner the following season. For biologists, monogamy implies selective (not exclusive) mating, a shared nesting area, and biparental care.


Young, L. J. (2003). The Neural Basis of Pair Bonding in a Monogamous Species: A Model for Understanding the Biological Basis of Human Behavior. National Academies Press (US). Retrieved from

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