Naturalistic fallacy

The naturalistic fallacy is usually seen as the inverse of the moralistic fallacy, though some see the latter as a variant of the naturalistic fallacy. Whether the one or the other is the case is not relevant in this blog, since here I want to discuss the reasoning error implied in the naturalistic fallacy; not its philosophical status.
Someone commits a naturalistic fallacy if this person argues that if something is natural it must be good or it ought to be. That is the positive version of the naturalistic fallacy, for just like for the moralistic fallacy, there is also a negative version. It says that what is not natural must not be good or it ought to not be. So:

X is, therefore X is good.
or
X is, therefore X ought to be.
and
X is not, therefore X is not good.
or
X is not, therefore X ought not to be.

The term “naturalistic fallacy” was coined by G.E. Moore in his Principia Media (p. 62). Moore argued that what is natural must not be confused with what is good, and that natural and normative properties are metaphysically different. With Ryle, we can say that they belong to different metaphysical categories and that we would make a category mistake, if we would deduce the one from the other. However, Moore was not the first philosopher who discussed the naturalistic fallacy. Already Hume argued that it is not allowed to jump from is to ought statements. On the other hand, even famous philosophers commit this fallacy, like John Stuart Mill, who argued that “human nature is so constituted as to desire nothing which is not either a part of happiness or a means of happiness”, and therefore “happiness is the sole end of human action, and the promotion of it the test by which to judge all human conduct; from whence it necessarily follows that it must be the criterion of morality.” (from McCraw, p. 193; italics mine)
Or another example:
“Nature gives people diseases and sickness; therefore, it is morally wrong to interfere with nature and treat sick people with medicine.
Explanation: If we break this down, we can say that the claim that nature gives people diseases and sickness is a declaration of what is (i.e., a natural property of the world). From this, we are deriving an ought (i.e., we ought not interfere...). The wording and order of these arguments can be confusing, but remember that the underlying fallacy here is the deduction of an ought from an is.
[However,] we go against nature (or what is) 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.” (source)
Sometimes it seems that “a naturalistic claim or property to a normative one won’t be fallacious or defective.” (McCraw, p. 195). McCraw discusses a few examples, but to my mind then in fact something else is the case. Instead of discussing McCraw’s examples, I want to take one that is more relevant to the current world situation, in order to make this clear.
I think that many of my readers will agree with the claim that the natural environment is deteriorating rapidly and therefore we ought to stop it. Nevertheless, at first glance, this argument seems to be false, since it is a clear case of a naturalistic fallacy. The reasoning is “fallacious or defective”, to use McCraw’s words, and I think that taken literally it is. However, one can read this sentence also as an elliptic statement, which stands for much more than what these thirteen words literally say. To make this clear, let me split up the statement into two parts: (1) The natural environment is deteriorating rapidly and (2) We ought to stop it. Then (1) is a summary of the state of the natural environment as described by many climate researchers, biologists, etc. and (2) summarizes the view or opinion of many people who think that the environmental degradation is bad for the world and for ourselves, and therefore ought to be stopped. So, (1) is a factual statement and (2) is a normative statement. Seen as a logical statement, the argument “(1) therefore (2)” is a naturalistic fallacy, indeed. However, seen as a practical statement, the argument “(1) therefore (2)” is sound, for a practical argument reasons what must be done on the basis of the known facts and our views. Therefore, if an argument reasons from a natural fact or a statement about what is natural to what ought to be done or what is good, first we must decide whether it is a logical or a practical argument, before we can say whether or not it is a naturalistic fallacy. Only as a logical argument it can be a naturalistic fallacy. As a practical argument it says what must be done. Of course, a practical argument can be unsound or false, but then for other reasons.

Sources and further reading
- Ethics Explainer: Naturalistic Fallacy
- McCraw, Benjamin W., “Naturalistic Fallacy”, in Robert Arp; Steven Barbone; Michael Bruce (eds.), Bad arguments. 100 of the most important fallacies in Western philosophy. Oxford, etc.: Wiley Blackwell, 2019; pp. 193-195.
- Naturalistic Fallacy, in Logically Fallacious
- Naturalistic Fallacy, in Wikipedia