I like some of the comment which has been passed here about the importance of great songs rather than great songwriters. For me a great song has above all else resonance. That's why very often the simple sounding ones - such as the ones Amos mentioned - are the ones which matter most to people. I don't actually create anything - rather I try to listen to what is going on in my head. It is not really a song until it sounds natural. Sometimes it happens in minutes and other times you have to carry the thing around with you for years. I try hard to listen to what's going on above all. After all, I don't really create the things, I'm just the lucky (or deluded) sod who gets to write them down. Plenty of writers of good songs are quite unexeptional at anything else - including other forms of writing. I think the craft is about listening above all.