Both English and Irish fiddling employ a certain amount of harmony through double stOpping.
THE ORIGNAL POSTER Quote
I've noticed that in the trad music I listen to, Irish groups are more likely to play their fiddle tunes straight, without any harmonizations, whereas English groups are more likely to add harmony and counterpoint lines. Is this a common difference between the two styles? Or is it just the specific groups I listen to?
So we were asked about fiddling and harmony., AND THEIR RELATIONSHIP according to the article Dave The Gnome provided, stated English fiddlers used different tunings as did shetland fiddlers
https://www.youtube.com/watch?v=4Or3Zdd-T2c
Above You tube clip on cross tuning on fiddle