Chomsky, like all good politicians, has changed his mind on how the mind works.

His original theory was that brains are equipped with a "universal grammar" that predisposes us to learn languages, and that the sentences of a language can be accounted for by a set of rules (its grammar). Now he believes that there is no universal grammar, just a circuit in the brain that is more or less plastic: change the connections and you get one or the other language. He also believes that we are equipped not with an innate knowledge of language but with a virtually infinite set of concepts. There are no rules of grammar, but there are associations between sounds and concepts: we learn a concept when we make the connection with a sound. Basically, we "rediscover" concepts that we have always unconsciously known (they have always been in our mind, since, presumably, prehistoric times).

But, like all politicians, he hasn't quite changed his mind for real. His innate brain circuit is not so different from his original idea of the innate universal grammar: it is just the same idea updated to the era of neuroscience (and renamed "I-language"); and so is his proposal that the brain already contains all possible concepts.

The problem is that his new theory of language is no longer capable of explaining why English sounds like English and not like Spanish. I can come up with an infinite list of words and sentences that just don't sound English. What is it that makes them "un-English"?

Chomsky is probably correct in stating that the "rules" of grammar are only a consequence, a side-effect, of the way language works. One could come up with a set of rules of how a muscle or a stomach works, but it is not that the brain has rules on how to run the muscle or the stomach: the rules are a way to explain what actually happens. They key is to discover the mechanism that generates those apparent "rules" of behavior (and their countless exceptions).

Most linguists simply neglect history and the fact that we are a species capable of learning and of transmitting knowledge. Were we a species that does not change over the centuries, Chomsky's original theory of language might have worked. Alas, we keep changing our culture and our behavior, and we instruct our children to maintain our changes. Whatever human phenomenon we observe we are bound to be confused by our own messing with it over the millennia. There might indeed be simple mechanisms that explain language, but those mechanisms are probably perturbed by the fact that humans continuously change their own culture, including their own language. Thus, at every point in time, one can find countless exceptions to every rule. Those exceptions are probably a sign that language is in progress, changing as we observe it. Imagine if you had to study the behavior of a machine while the machine is being dismantled and rebuilt. That is what we do when we study any human phenomenon.

A study of the history of language would probably show that there are many more regularities than one supposes irregular verbs probably have a reason to be what they are (they may have been regular in the past, according to a long-forgotten rule), words may be derived from very simple sounds, idiomatic expressions may be based on bodily features, etc. If one studies history, there might be simple explanations for everything. If one takes the human world as it is today and tries to make sense of it, the task is virtually impossible.

It is not that Chomsky was wrong then or is wrong today: it is just that Chomsky is not studying what he says he is studying.