From the revolutionary first wave feminism in the 18th century to the contentious LGBT issues today, it is generally accepted that gender discrimination has reduced over the years. It continues, however, to plague societies today. One of the many factors behind the persistence of gender discrimination is the idea that how the different genders and sexes should behave is determined by their nature. In gender and sexuality debates, it is not uncommon to encounter arguments such as these:
- ‘Men and women should not have the same roles in society because men have more muscle mass and women can give birth.’
- ‘Men are naturally more aggressive and competitive while women are naturally more nurturing and cooperative. Therefore, aggressive and competitive domains (such as politics) ought to be the province of men, and nurturing and cooperative domains (such as childrearing) ought to be the province of women.’
- ‘Homosexuality is unnatural. Therefore, it is immoral.’
- ‘Adultery is acceptable because people naturally want more sexual partners.’
It is interesting to note that these arguments share a common feature, namely that they claim that a certain practice is good or right because it conforms to certain facts of the world, or that a certain practice is bad or wrong because it does not conform to certain facts of the world. Although such arguments may sound plausible because their recommendations are based on verified or verifiable facts, some philosophers find them suspect. In fact, such an argument pattern has become so common that its critics devised labels for them, including the naturalistic fallacy, the is-ought fallacy, and the appeal to nature fallacy. The popularity of such arguments is not hard to discern: if it can be shown that certain values are based purely on facts about nature, especially scientific facts, then these values can be deemed objective and those who reject these values can be deemed irrational. Yet, some philosophers point out that what is natural may not be morally right, and conversely, what is unnatural (artificial) may not be morally wrong. And they conclude that arguments that base moral rightness or wrongness solely on what is natural or unnatural (artificial) is suspect.
The term ‘naturalistic fallacy’ was coined by British philosopher G. E. Moore in his Principia Ethica, where he argues that it would be fallacious to explain define moral properties such as good reductively, in terms of natural properties such as pleasant or desirable. Moore’s naturalistic fallacy is closely associated with the is–ought fallacy originating in Scottish philosopher David Hume’s A Treatise of Human Nature, where he argues that it is questionable to conclude that something ought to be in a certain way just because something is in a certain way. More recently, the naturalistic fallacy and the is-ought fallacy are used synonymously with the appeal to nature fallacy, exemplified by reasoning forms such as ‘something is morally right because it is natural’ or conversely, ‘something is morally wrong because it is unnatural’. The relationship between the is-ought fallacy and the appeal to nature fallacy can be understood as one between a set and a subset. As ‘natural’ can be seen as a specific case of ‘is’ and ‘moral rightness/wrongness’ can be seen as a specific case of ‘ought’, the appeal to nature fallacy can be seen as a subset of the is-ought fallacy. In what follows, I shall focus only on the appeal to nature fallacy.
Why should we be suspicious of appeal to nature arguments? Referring to the examples above, we can see how appeal to nature arguments are used to show that adultery is morally acceptable by claiming that it is what people naturally want, or that women should stay at home and take care of children because they are naturally better nurturers. If such arguments are not deemed fallacious, we will have to show that the premises – adultery is what people naturally want and women are naturally better nurturers – are empirically false to refute the arguments. Yet, the premises seem empirically true and so they seem to offer good empirical reasons to accept the conclusions, even if the conclusions may have morally questionable or unacceptable consequences. This led some philosophers to suspect that something is amiss about such arguments. Being suspicious of such arguments encourages us to examine what exactly is wrong with them. Why is it that their premises seem empirically true and relevant and yet the conclusions seem questionable and unacceptable?
In his book Making Sense: Philosophy Behind the Headlines, Julian Baggini provides a simple answer: ‘Even if we can agree that some things are natural and some are not, what follows from this? The answer is: nothing. There is no factual reason to suppose that what is natural is good (or at least better) and what is unnatural is bad (or at least worse)’. A more in-depth answer is provided by Charles Pigden in his article “Logic and the Autonomy of Ethics”. In it, he argues that logic is conservative, which is roughly the idea that in logic, you cannot get out what you have not put in. More precisely, if you have not put moral components into the premises, you cannot get moral components out in the conclusion.
A culinary metaphor may help to clarify Pidgen’s point. If you want to cook a sweet dish, you have to add sweet ingredients. You cannot cook a sweet dish with only salty ingredients. Likewise, you cannot get a moral conclusion from only natural premises, you need moral premises too, whether or not they are made explicit. Two qualifications need to be made here. First, natural premises can still be used to derive a moral conclusion so long as at least one moral premise is included. Second, some natural premises may contain implicit moral components. To extend the culinary metaphor, it is possible to make a sweet dish with both sweet and salty ingredients, and it is also possible for a single ingredient (such as seasoning powder) to be both sweet and salty.
So how should we fix appeal to nature arguments? From the above discussion, we can infer two ways to fix appeal to nature arguments. First, we can either add a moral premise or make an implicit moral judgement contained in the natural premises explicit. Second, if the first fix cannot be done because no moral components are included in the premises, then we can revise the conclusion from a moral claim to a natural claim. Let’s consider one of the above examples:
- Homosexuality is unnatural. (Natural premise)
- Therefore, homosexuality is immoral. (Moral conclusion)
Of course, it can be shown that the natural premise is false because homosexuality does exist in the animal kingdom. But showing that the natural premise is false does not fix the appeal to nature argument. To focus on applying the first fix, assume that the natural premise is true and look for implicit moral components in the premise. There seems to be a hidden or suppressed moral premise, which is:
- Whatever is unnatural is immoral (Moral premise)
Once the natural premise (Homosexuality is unnatural) and the hidden or suppressed moral premise (Whatever is unnatural is immoral) are combined to derive the moral conclusion (Therefore, homosexuality is immoral), the argument no longer commits the appeal to nature fallacy; it becomes logically valid. Of course, the author of the argument must now justify the moral premise, which is vulnerable to many counterexamples. Many things are unnatural but not immoral (humans use technology pervasively in their daily lives; conversely, many things are natural but not moral (some animals eat their own young).
For the second fix, let’s consider another of the above examples:
- Men have more muscle mass and women can give birth. (Natural premise)
- Therefore, men and women should not have the same roles in society. (Moral conclusion)
Of course, there are questionable implicit moral components in the premise (such as you should go out and work if you have more muscle mass and you should stay at home if you can give birth). But to focus on applying the second fix, assume that the author of the argument does not intend any moral component in the premise. In this case, the author commits the appeal to nature fallacy if he intends a moral conclusion, which makes his argument logically fallacious. To fix his argument, the author needs to modify his conclusion from a moral one to a natural one such as:
- Therefore, men and women are expected to have different roles in society. (Natural conclusion)
Once the argument derives a natural conclusion from a natural premise, it no longer commits the appeal to nature fallacy; it becomes logically cogent. Of course, it is still possible for the conclusion to be empirically false, for there may be societies where the majority of the women go out to work instead of staying at home and the majority of the men stay at home instead of going out to work.
The appeal to nature fallacy in gender and sexuality debates is still prevalent in the public domain. It is hence useful to know what it is, why we should be suspicious of it, what exactly is wrong with it, and how to fix it.
 George Edward Moore, Principia Ethica, ed. Thomas Baldwin, (Cambridge: Cambridge University Press, 1973), 62.
 David Hume, A Treatise of Human Nature, eds. L.A. Selby-Bigge and P.H. Nidditch, (Oxford: Oxford University Press, 1978), 469-70.
 Julian Baggini, Making Sense: Philosophy Behind the Headlines, (Oxford: Oxford University Press, 2004), 181-82.
 Charles Pigden, “Logic and the Autonomy of Ethics,” Australasian Journal of Philosophy 67, no. 2 (1989): 127-151.