Just as empiricist accounts of learning are inadequate to explain children’s linguistic competence, so also are they inadequate to explain children’s moral competence (Dwyer 1999; Harman 2000). For example, children exhibit the capacity to make genuinely moral judgments since they are sensitive to the moral/conventional distinction in their use of terms like “wrong”. It has been shown that children as young as 3 years old will regard moral transgressions as more serious than conventional transgressions and regard the former as more universal, independent of any authority figure, and closely correlated with considerations of harm (Smetana and Braeges 1990; Smetana 1993; Nichols 2002a). So if children are told that some households have no rule against, say, running in the house or eating dessert before dinner, then even if their parents do have rules against these practices, most children will judge that it is not wrong for children who live in the households where the rules do not exist to do these things. However, children will judge that hurting another is wrong, even if they are told that some parents have no rule against hurting others. They make similar claims across different cultures. And this recognition emerges early in the developmental psychology of children – earlier than we should expect if children learn it only from explicit moral instruction from caregivers.
And here is the argument:
Absent a detailed account of how children extrapolate distinctly moral rules from the barrage of parental imperatives and evaluations, the appeal to explicit moral instruction will not provide anything like a satisfactory explanation of the emergence of mature moral competence. What we have here is a set of complex, articulated abilities that (i) emerge over time in an environment that is impoverished with respect to the content and scope of their mature manifestations, and (ii) appear to develop across the species (Dwyer 1999, 173).
Anyone familiar with the nativism in linguistics will notice some glaring problems with both the evidence and the argument presented here. First of all, the analogy to the poverty of stimulus argument in linguistics can't be meant to go very far. The Chomskyan version not only argues that children don't receive enough input to account for the level of sophistication in their early knowledge of grammatical principles, but also argues that no amount of input could account for this. I don't think this is the claim that ethicists want to make. Furthermore, the types of linguistic structures proposed to account for early grammatical knowledge, which generally consist of rules for the combination and movement of linguistic objects, are probably not the sorts of innate moral knowledge that ethicists would want to propose. Still, there are other, less Chomskyan versions of the poverty of stimulus argument, and not everyone buys the Chomskyan architecture either1. So, there may still be parallels between the two domains.
Still, even if we assume that ethicists don't mean that ethical knowledge cannot be learned, no matter what the input, the evidence and argument still suffer from several major flaws. Here are some of them:
All in all, I think the use of the poverty of stimulus argument in ethics is interesting, but premature. A great deal of research, and a better formulation, are needed before empiricists take such an argument seriously. Right now, I see no reason to think that an empiricist account of ethical development can't account for the data. Each of the problems listed above (with the possible exception of the last one) has been mirrored in the nativism debate in linguistics. For that reason, I think ethicists who want to make poverty of stimulus arguments in their field would do well to familiarize themselves with the linguistics argument and the trials it has gone through over the past few decades. The analogy to the linguistics version of poverty of stimulus may not be meant to go very far, but it can still be instructive in this way.
1 Ray Jackendoff's version of innate linguistic structure, for instance, differs markedly from Chomsky's. You can read about it in his excellent book, Foundations of Language: Brain, Meaning, Grammar, Evolution.
2 For instance, the work of Michael Tomasello on language acquisition, references to which can be found here. His book The Culturual Origins of Human Cognition presents the arguments in detail, though he has produced even more convincing evidence since its publication.
3 Zuidema, for instance, makes this argument in linguistics, in this paper.
4 See e.g., The Evolution of the Golden Rule, Gretchen Vogel, Science Feb 20 2004: 1128-1131.