  In this section, we will focus on features (v) and (vi) of the  pld. For it is consideration of the positivity of the data  set, and the lack of feedback available to children, that has given  rise to what I am calling the ‘Unlearning Problem,’  otherwise known (somewhat misleadingly) as the ‘Logical Problem of Language Acquisition.’ (For statements of the argument, see, e.g., Baker 1979; Lasnik; 1989:89-90; Pinker 1989.)