Learners' mistakes

Can you remember the two general catagories of mistakes made by learners?
Which one can often be self-corrected?

Take a look at these articles from http://www.teachingenglish.org.uk/ which gives a good overview of error correction.

http://www.teachingenglish.org.uk/articles/error-correction-1

http://www.teachingenglish.org.uk/articles/error-correction-2