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Naturalistic Fallacy

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(also known as: is-ought fallacy, arguing from is to ought, is-should fallacy)

Description: When the conclusion expresses what ought to be, based only on actually what is more natural.  This is very common, and most people never see the problem with these kinds of assertions due to accepted social and moral norms.  This bypasses reason and we fail to ask why something that is, ought to be that way.

This is the opposite of the moralistic fallacy.

Logical Form:

X is true according to nature.

Therefore, X is morally right.

Example #1:

Homosexuality is morally wrong because, in nature, sex is used for reproduction.

Explanation: We cannot make moral judgments based on nature -- unless that is your moral philosophy to do so, but then you really need to reevaluate what “moral” means if living by instinct and desire leads to moral behavior.  As for our example, the assumption is also made that sex is for reproduction only.

Example #2:

Nature gives people diseases and sickness; therefore, it is morally wrong to interfere with nature and treat sick people with medicine.

Explanation: We go against nature all the time.  We cannot sometimes use nature as a moral baseline and at other times condemn her for her careless attitude and indifference toward the human race.

Exception: At times, our morality will be in line with nature -- but if we are justifying a moral action, we need to use something besides nature.

Tip: Never be afraid to ask, “why”.


Pinker, S. (2003). The Blank Slate: The Modern Denial of Human Nature. Penguin.

Registered User Comments

Greg Waddell
Thursday, June 09, 2016 - 10:07:20 PM
Regarding the Homosexuality argument above. Would not the following argument also be an example of the naturalistic fallacy?
Homosexual activity cannot be morally wrong because we see examples of it in nature.

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Bo Bennett, PhD
Friday, June 10, 2016 - 08:55:13 AM
Yes, it would.

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