This document discusses error analysis in second language acquisition. It defines errors as systematic deviations from the rules of the target language, while mistakes are performance errors that can be self-corrected. Behaviorists viewed errors as a failure of learning, while mentalists saw them as inevitable parts of the language learning process. The aims of error analysis are to identify error types and patterns, establish taxonomies, and inform teaching. Errors can be interlingual from L1 interference or intralingual from faulty L2 learning. Error analysis contributed to understanding of language learning but also has limitations in methodology.