 Second, they provide the researcher with evidence of how language is learned or acquired, and what strategies or procedures the learner is employing in his discovery of the language.Third (and in a sense this is their most important aspect) they are indispensable to the learner himself, because we can regard the making of errors as a device the learner uses in order to learn (p. 167).The occurrence of errors is merely signs of ‘’the present inadequacy of our teaching methods’’ (Corder 1976, p. 163).