Psychologically speaking, all linguistic behavior is the overt manifestation of some type of underlying knowledge that is represented in the mind/brain of an individual. Exposure to linguistic data is necessary for growth of the system of knowledge. On the basis of only overt linguistic behavior, how can we ascertain whether the native and nonnative knowledge systems that people have are of distinct or similar types? Is there a (necessary) relationship between type of knowledgeand type of linguistic exposure?
The hypothesis to be defended is that negative data and explicit data result in a type of knowledge that is not to be equated with linguistic competence. The claim is not that negative and explicit data cannot give rise to knowledge; rather, the specific claim is that only positive data can effect the construction of an interlanguage grammar that is comparable to the knowledge system that characterizes the result of first language acquisition.
