The notion of Universal Grammar (UG) is generally understood to embody a particular hypothesis, namely, that some substantial portion of human language is based on universal domain-specific syntactic principles that are biologically determined (“innate” or unlearned). The UG Hypothesis thus involves four interrelated claims:

1. 1. Domain-specificity: Language acquisition is constrained by representations or principles that are specific to language.

2. 2. Universality: These representations or principles are universal.

3. 3. Innateness: These representations or principles are not learned.

4. 4. Autonomous syntax: These representations or principles require reference to syntax, not to possible functional correlates of syntax.

Versions of each of these claims, taken independently, are not at all controversial. As Christiansen & Chater (C&C) make clear, no one believes that language arises from nothing. Our biological endowment is what separates us from the Amazon horned frog and is what ultimately ensures that humans have language while frogs do not. This is not the issue; the question is whether what separates us includes unlearned linguistic (i.e., domain-specific) representations concerning syntax. Generalizations about universals of human conceptual structure or about the human vocal tract do not provide evidence of Universal Grammar insofar as Universal Grammar is understood to be about grammar.

It is likewise clear that learning itself requires prior biases of one sort or another, since without any a priori similarity metrics or attentional biases, a system would not know on what basis to generalize; all input would be weighted equally or in some random fashion. But again, this general fact in no way requires that the metrics or biases must be domain-specific. Clearly, too, everyone recognizes that there are some language universals; the question is whether the universals make reference to autonomous syntactic generalizations, or whether instead they are explicable in terms of domain-general abilities and/or the semantics or pragmatics of the constructions involved (cf. Bates Reference Bates1993; Goldberg Reference Goldberg2006; Newmeyer Reference Newmeyer2005, for relevant discussion). In addition, we can all agree that adults have representations that are specific to language (for example, their representations of individual constructions); the question is whether these representations can be learned.

“Universal Grammar” has alternately been interpreted, not as a hypothesis, but as a definitional label. It can be defined as the “initial state” of the child before exposure to language, or as the set of constraints that narrows the set of all logically possible languages to the set of all humanly possible languages. Neither of these interpretations of UG embodies a controversial claim. Surely infants (at least younger prenatal) can be said to be in some initial state before they are exposed to language. Certainly there are constraints on the range of possible human languages. On either of these interpretations, once again, UG may not be specificallyabout grammar at all. The initial state and the set of factors that constrain human language may be comprised entirely of domain-general abilities and mechanisms that conspire to give rise to the inclination and ability to create, learn, and use language.

Everyone also understands that language must be compatible with the human brain in that processing mechanisms and social forces are recognized to constrain language.Footnote ¹ Chomsky himself has recently emphasized the role of domain-general processes. In fact, he has acknowledged that he remains unconvinced by any proposals for domain-specific innate syntactic representations or principles, with the (possible) exception of recursion, noting, “We hypothesize that FLN [the domain-specific Faculty of Language] only includes recursion” (Hauser et al. Reference Hauser, Chomsky and Fitch2002, p. 1569).Footnote ²

The target article by C&C highlights the challenges that defenders of the four interrelated claims (listed above) face in detailing how unlearned, communicatively arbitrary universals of grammar might have evolved (see also, Deacon Reference Deacon1997; Elman et al. Reference Elman, Bates, Johnson, Karmiloff-Smith, Parisi and Plunkett1996). Moreover, while it made sense for researchers to explore the UG Hypothesis at the time it was proposed (Chomsky Reference Chomsky1965), we are now in a better position to appreciate the power of statistics, implicit memory, the nature of categorization, emergent behavior, and the impressively repetitive nature of certain aspects of the input.

In order to avoid prejudging whether any of the necessary abilities and constraints on language are domain-specific (specifically syntactic), a better term than Universal Grammar might be Prerequisites for Natural Language. As Liz Bates used to say, “It's not a question of Nature vs. Nurture; the question is about the Nature of Nature” (Bates Reference Bates1993).

Of course, if universal syntactic representations have not evolved biologically, then various questions immediately come to the fore, many of which are briefly discussed by C&C. What domain-general processes account for each cross-linguistic regularity? Why are there impressive generalizations within any given language? What distinguishes us from other primates such that only we spontaneously create and learn language? How exactly is language learned and processed? More generally, what exactly are the Prerequisites for Natural Language and how do they interact to yield the constrained complexity that is language? These are exactly the questions that are currently the focus of a tremendous amount of ongoing work (cf. references in the target article).