  I also set aside features (iii) and (iv). For one thing, it is  unclear exactly how degenerate the pld are; according to one early estimate, an impressive 99.7% of utterances of mothers to their children are grammatically impeccable (Newport, Gleitman and  Gleitman 1977). And even if the data are messier than this figure  suggests, it is not unreasonable to suppose that the vast weight of  grammatically well-formed utterances would easily swamp any residual  noise. As to the idiosyncrasy of different children's data sets, this is not so much a matter of stimulus poverty as stimulus difference.  As such, idiosyncrasy becomes a problem for a non-nativist only on  the assumption that different children's states of linguistic  knowledge differ from one another less than one would expect given  the differences in their experiences. As far as I know, no serious  case for this last claim has ever been   made.[12] 