Two heads, hands, voices, opinions can work better than one- but it matters deeply what each brings to the duo. Contrast of voice, instrumentation, taste often creates a synergy that far transcends what each does solo. If you don't know the performers as solo, it might be hard to see where the magic in a duo happens.

In the superb on their own / better together category :
Anne Hills & Cindy Mangsen
John Roberts & Tony Barrand
Liam Clancy & Tommy Makem

Perhaps part of it is patter & interaction when they perform, but I think that bringing different points of view to songs or tunes causes a different thought process. Why do a song this way? Why play this instrument? Debate brings up fresh perspectives.

I've had the delight of watching two long time friends and musicians grow a duo. I've listened to Phil Cooper for years as part of a duo/trio/ensemble, with singing partner Margaret Nelson as the constant through all those years. Phil's darlin Susan wrote wonderful songs, sang wacky and ribald songs she'd found elsewhere and became an ever more deft musician through those years. Now they're a duo - February Sky - and the combination of Phil's incredible repertoire of very traditional song and tune and Susan's singer-songwriter orientation and addition of her skill with other instruments have been blended into something very different than what either had done before. Same songs, or tunes from previous repertoires... but whole different flavor. Each time I see them, what they do gets tighter, deeper, more distinctive.

'Course it helps that both are thoughtful, generous people who like each other lots.

Joanne in Cleveland