  For as we have seen, the pld is mostly just a sample of  sentences, of positive instances of the target language. It contains  little, if any, information about strings of words that are not  sentences. For instance, children aren't given lists of ungrammatical strings. Nor are they typically corrected when they make mistakes.  And nor can they simply assume that strings that haven't made their  way into the sample are ungrammatical: there are infinitely many  sentences that are absent from the data for the simple reason that  no-one's had occasion to say them yet.