During the 1970s:
The research goal was to discover what learners really know about the TL. Their errors reflect their current understanding of the rules and patterns of the TL.
Error analysis replaced contrastive analysis. It did not set out to predict L2 learners’ errors; rather, it aims to discover and describe different kinds of errors in an effort to understand how learners process the L2.
Error analysis is based on the assumption that L2 learner language is a system in its own right – one which is rule-governed and predictable.