The 'right Key' is conceded to be the singer's Key. Most tunes and songs have more than one version or interpretation, which are melodic and/or rhythmic variances from 'how it was written' or 'what you are used to hearing'. Looking at song transcriptions is is not unusual to see a part of the melody written as e.g. a half-note in one verse and as two quarter-notes in another verse to correspond to one word versus two words. Many musicians (and even singers) will add different ornamentations which can add, subtract, and/or change notes. Whether it is the same tune/song has to do with the overall 'sound', minor differences don't change the basic melody. Yes, most tunes/songs tend to be played in a certain Key. I think that is because of how the notes fall on the instrument(s) it was written on and/or tend to be played on and/or sung in. What Key is it? That is determined by what note the tune/song resolves to and how many flats/sharps there are (the Key Signature) - this is really just a matter of what it is called. I've found most Music Theory instruction to be confusing, recently I think I've managed to sort it out - I'll start a new message thread with my take on it. Michael