Alsystem of knowledge about a second language which goes well beyond what could possibly have been taught .Patterns of recurrent elements that comprise components of L2 - specific knowledge : vocabulary ( lexicon ) , morphology ( word structure ) , phonology ( sound system ) , syntax ( grammar ) , and discourse ( ways to connect sentences and organize information ) .How to encode particular concepts in the L2 , including grammatical notions of time , number of referents , and the semantic role of elements ( e.g. whether subject or object ) .