Errors and mistakes: These are terms teachers and students commonly use interchangeably to describe those little foul-ups occurring in written and oral communication. In SLA, however, they are not considered interchangeable (Ellis 17). Errors can only occur when a learner does not already know a particular language principle; it signifies a gap in their learner language.
Example: I goed to the baseball game.
If the learner does not realize that the English go is an irregular verb, and consequently overgeneralizes with the regular -ed ending, this is a learner error.
Mistakes occur in spite of what a learner knows; they signify a temporary lapse in linguistic ability (Scovel 48).
Example: Sorry I am late, professor. I get lost coming to class.
Technically, it should have been “I got lost coming to class.” Whether or not this is an excuse is not the issue at hand. The real question is, Is this a mistake or an error? Does the learner ever use “got” correctly? Do they ever use the past tense? Is this part of a pattern (error) or a deviation from it (mistake)?
Ellis, Rod. Second Language Acquisition. Oxford, 1997.
Scovel, Tom. Learning New Languages. Heinle & Heinle, 2001.