As children mature, they acquire many things: teeth, languages, toys, viruses, friends, habits, secondary sexual characteristics, drivers’ licences, etc. With regard to some of these—e.g., teeth—all normal children follow a common developmental path that ends in a mature state, allowing for individual variation within narrow limits. Each child acquires her own teeth, which at some level of detail, exhibit a unique cluster of properties: sizes, shapes, gaps, susceptibility to cavities, etc. But no child acquires thirty-seven shark teeth. On the whole, parents and dentists know what to expect. Teeth emerge gradually—starting in the second half of the first year after birth, with the full set of “primary” teeth manifesting in the next two years—and then kids lose their first set, starting around age 7, as their “permanent” teeth start to emerge.
In some respects, language acquisition is similar. But acquired languages, in contrast to teeth, vary in ways tracked by linguistic experience. Kids tend to acquire the languages they are exposed to. (Exposure to English doesn’t yield competence in Japanese.) Another difference is that normal human beings don’t have opinions about odontogenesis. Which is just as well, since we’d get it wrong. Tooth development is a complicated business, starting around 14 weeks after conception, with roots and crowns continuing to morph for a while even after the teeth have “erupted.” By contrast, people are apt to have untutored opinions about how kids acquire languages. And this can influence how theorists describe language acquisition. In particular, it’s often taken to be obvious that kids acquire languages by learning them. This little theory often masquerades as common sense, thereby avoiding critical scrutiny. But let’s remove the mask.
Historically, the little theory has been combined with very implausible assumptions about animal psychology, and an inchoate version of the idea that humans acquire E-languages; see, e.g., Word and Object. But one can hypothesize that kids acquire I-languages by learning them.
The ‘by’ is important here. One can describe I-language acquisition as a kind of learning. One can also describe walking as a kind of locomotion. But walkers don’t walk by locomoting; the fact that walkers locomote doesn’t explain how walkers walk. With this in mind, imagine an alien who wants to know how human children acquire I-languages: do I-languages emerge like teeth; do kids spontaneously create the generative procedures, perhaps after being given a pill; do kids download local I-languages via The Cloud; are I-languages somehow contagious?
Suppose the reply is that kids acquire I-languages by learning them, and that this is why acquired I-languages vary in ways tracked by linguistic experience. The alien will surely ask how kids learn procedures (as opposed to skills). So one might explain Universal Grammar (UG) and offer this idealization: if L is the UG-compatible I-language used in community C, then kids born into C learn that L is the UG-compatible I-language used in C. But then the alien will ask if there isn’t a distinction between (i) learning L and (ii) learning that L is the language that members of C are using, given prior assumptions about which languages they could be using.
A less polite alien would complain that it’s a bait-and-switch to say that kids acquire languages by learning them, and then treat instances of (ii) as instances of (i). But for today, let’s suppose that kids in Topeka acquire English as opposed to Japanese/Finnish/etc. because they somehow learn which (UG-compatible) I-language is “locally dominant,” while kids in Tokyo acquire Japanese as opposed to English/Finnish/etc. because they likewise learn which I-language is locally dominant. Still, it’s one thing to explain why a child acquires English as opposed to Japanese. It’s another thing to explain how the child acquires an I-language at all, and English in particular. So getting back to the little theory, one question is whether a child who acquires L does so by learning that L is the locally dominant I-language.
In principle, one can imagine a positive answer. For L might serve as a “target” in either or both of two senses. A child might start with a “proto-I-language” P, use it as a simple initial model of the locally dominant I-language L, and use experience to successively adjust P in ways that eventually lead to instantiation of L. Or a child might use symptoms of L to determine values of variables in an evaluation procedure that selects L from a space of candidates for being the locally dominant I-language. The first idea is that kids successively approximate L. The second idea is that kids compute which I-language is locally dominant. Either way, L looks like an E-language from an acquirer’s perspective: L is represented as an aspect of the acquirer’s environment. And familiar difficulties beset attempts to approximate generative procedures that exhibit constrained homophony, or infer such procedures from detectable parameter values. A more attractive option, in my view, is that acquired languages are not targets in either sense.
Charles Yang shows how choices for parameter values can be rewarded/punished by experience in ways that lead acquisition devices to converge on what theorists (not the devices) describe as a target grammar. I think Yang’s models shed real light on how kids stabilize on a local I-language. We can even speak of Yang-learning that L is the locally dominant I-language. And clearly, some aspects of L (e.g., how to tense verbs) are learned in some sense. But a Yang-learner doesn’t acquire L by learning that L is the locally dominant I-language. A system of this sort is not in the business of discovering what other systems are doing. It has a procedure for replacing the I-language(s) it uses—under pressure from apparent failures of comprehension and/or communication—without representing or trying to acquire anybody’s I-language.
This coheres with my general hunch that I-languages play an important role in human cognition prior to their use in communication. Suppose that I-languages are basically the same on the meaning side, and some I-language (perhaps phonologically null, with a limited lexicon) will emerge naturally in a child, at least given a few gruntings by conspecifics. That might be enough for certain intrapersonal uses. But for interpersonal communication, a child will need to trade in the “starter I-language” for something a bit flashier, and then keep trading up until she hits on an I-language that supports communication well enough (or until the critical period ends).
This coheres with the phenomenon of creolization. Kids can acquire an I-language that had never been acquired before. That’s bad news for the theory that kids acquire I-languages by learning them. One can say that creolizers try to acquire the locally dominant (UG-compatible) I-language, and end up with what they end up with, as on a quest for the grail. But in any case, kids can acquire an I-language that wasn’t there to be learned. And whoever first acquired (UG-compatible) I-languages didn’t learn them. Those humans may have been kids who heard parental grunting, and then found themselves talking to each other in ways the parents couldn’t follow. One can hypothesize that even these pioneer creolizers were trying to acquire the locally dominant I-language. (Quite an evolutionary trick: emergence of a capacity to learn I-languages before there were any to learn.) But in any case, the pioneers’ descendents have the same power to create I-languages where there are none to learn. So why think that humans ever started to acquire I-languages by learning them? Maybe kids kept doing what the pioneers did, just in response to fancier gruntings. (That coheres with the “continuity” hypothesis discussed here.)
Of course, there’s no guarantee that an I-language L that lets you talk with your peers will let you talk to your kids in ways that will get them to acquire L. And the I-languages currently in stable use are “heritable” in this sense. But any “unheritable” I-languages wouldn’t remain in use for long. So maybe we shouldn’t be too impressed by the fact kids typically acquire the locally dominant I-language (as opposed to a significantly different variant). It may be that the counterexamples to this generalization quickly die out.