This is a good question because sometimes there is not a lot of difference between the two. Basically I would agree with what FDG mentioned, plus I would say that each type might have a strong role function (or might me weak, in which case it would not be difficult to tell them apart), but each of them may be more reckless about it than if it was their strength. It is not anything that I could explicitly explain, but rather it is something that you would have to catch on to after meeting enough EXTp’s.