  Chomsky (e.g., 1965: 30-31) expresses this last point in terms of the need for constraints — on grammatical concepts, on the hypothesis space, on the interpretation of data — and proposes  that it is innate knowledge of UG that supplies the needed  limitations. On this view, children learning language are not  open-minded or naïve theory generators — they are not  ‘little scientists.’ Instead, the human language-learning mechanism (the ‘language acquisition device’ or  ‘LAD’) embodies built-in knowledge about human languages, knowledge that prevents learners from entertaining most possible  grammatical theories. As Chomsky puts it: