For example, most universal grammar approaches postulate that a child forms a question by following a set of rules based on grammatical categories such as “What (object) did (auxiliary) you (subject) lose (verb)?” Answer: “I (subject) lost (verb) something (object).” If this postulate is correct, then at a given developmental period children should make similar errors across all wh-question sentences alike. But children’s errors do not fit this prediction. Many of them early in development make errors such as “Why he can’t come?” but at the same time as they make this error — failing to put the “can’t” before the “he” — they correctly form other questions with other “wh-words” and auxiliary verbs, such as the sentence “What does he want?”

Experimental studies confirm that children produce correct question sentences most often with particular wh-words and auxiliary verbs (often those with which they have most experience, such as “What does…”), while continuing to make errors with question sentences containing other (often less frequent) combinations of wh-words and auxiliary verbs: “Why he can’t come?”

The main response of universal grammarians to such findings is that children have the competence with grammar but that other factors can impede their performance and thus both hide the true nature of their grammar and get in the way of studying the “pure” grammar posited by Chomsky’s linguistics. Among the factors that mask the underlying grammar, they say, include immature memory, attention and social capacities.

Yet the Chomskyan interpretation of the children’s behavior is not the only possibility. Memory, attention and social abilities may not mask the true status of grammar; rather they may well be integral to building a language in the first place.