  But suppose that the child is predicting not strings of words,  simpliciter, but rather strings of words under a certain syntactic description (or, perhaps more plausibly,  quasi-syntactic description — the categories employed need not  be the same as those employed in adult   grammars).[14]  This would enable her to make much better use of non-occurrence as  negative evidence. For non-occurring strings will divide into two  broad kinds: those whose structures have been encountered  before in the data, and those whose structures have not been heard before. In the former case, the child has positive evidence  that strings of that kind are grammatical, evidence that would enable her to suppose that the non-occurrence of that particular string was  just an accident. (E.g., she could reason that since she's heard  Is that mess that is on the floor in there yours? many  times, and since that string has the same basic structure as Is  that girl that's in the jumping castle Kayley's daughter?, the  latter string is probably OK even though Dad chose not to say it.)