This is the old chestnut which comes out every year! When I joined this list around 7-8 years ago, I was corrected by one of our erstwhile antipodean lutenists thus..
Thumb-in = Early lute technique (fast-runs and fewer courses) Thumb-out = Later lute technique (More bass strings to contend with) Thumb-over = Guitarist's cheat for playing F-major Thumb-under = An illegal move in Rugby Football Best Wishes Ron (UK) Jon Murphy wrote: I was recently emailed a couple of paragraphs from a lute instructional regarding the right hand - it spoke of "thumb under" and "thumb over". Now then, is thumb in/out another way of saying the same thing - or a different thing entirely.