There's always the fear, when writing tunes, that you will write a tune you've heard in the past. I know I've done it a couple of times. This is the reason I usually play new tunes to friends who have a wide repetoire, in the hope or fear they'll recognise it. If they join in the first time through, there's cause for concern!

Pentatonic tunes are great - Spootiskerry by Ian Burns is a good example with just one passing note going onto the white notes. And it's a tune which took me about ten minutes to learn.

As lefthanded guitar said, some tunes just seem natural and these are the ones that cause me the most concern - is this a tune I've heard in the past and stored in the dim recesses of my head?

Tunes which flip between major and minor at irregular intervals like some of the Scandinavian tunes I find a real pleasure to write and I think they are good. If I don't, then who will?