This hypothesis  explains how acquisition and

learning are used; the acquisition system, initiates an utterance and the

learning system ‘monitors’ the utterance to inspect and correct errors. 

Krashen states that monitoring can make some contribution to the accuracy of an

utterance but its use should be limited.  He suggests that the ‘monitor’

can sometimes act as a barrier as it forces the learner to slow down and focus

more on accuracy as opposed to fluency.