Ellis (2000) considers that an error happens when the deviation arises as a result of lack of knowledge。 It represents a lack of competence。 A mistake occurs when learners fail to perform their competence, it occurs occasionally because of the lapses in performance。 The learner knows the language point but fails to work it out in its correct way in a particular situation。 

Carl James (2003) makes his point about distinction between error and mistake in his book Errors in Language and Use。 If the learner is willing and able to correct a fault in his output, it is regarded that the sentence or word he used is not the one he intended, and we can say that kind of fault is a mistake。 However, if the learner is unable or disinclined to correct the fault, we assume that the sentence or word the learner used is the one he intended and that is an error。