I was watching a barney kessel interview and he was talking about his guitar playing style, and he said a way to make a melody sound more 'full' is to harmonize the melody using different intervals, like harmonizing 'in thirds' or 'in sixths' or whatever. Does harmonizing a melody in thirds mean you play notes that are a 3rd above the melody part, or play notes where the original melody would be a third above what you're playing..
it could be either one