knowing a language is different from using that knowledge,"knowing a language "means knowing what sounds are part of the language and how these sounds combine to form words. it means being able to understand other sentence spoken in that language. In short,it means knowing the "rule" of the language. This kind of knowledge of a language is called linguistic competence. This kind of (or competence)is very difference from actually using
a language.When we speak we often use in complete sentence,or don't finish sentence,make mistakes in sounds or grammar,and so forth.For example, an english speaker might accidentally say "you missed my history lecture."This real speech behavior is called linguistic performance