Above it was said that the voice should be suited to the kind of music. I couldn't agree more. It makes about as much sense to have Beverly Sills sing "Can't No Grave Hold My Body Down" as it does to have Jo Stafford (I totally agree, Art!) sing "Sourwood Mountain". Each could do the job. But their vocal styles are not best suited to the purpose. By the same token, I doubt that Ronnie Milsap could do a very good job with a Wagner opera. Nor could Ian and Sylvia (together or separately) do very well with "Speak Low".

This isn't to say that with training, someone couldn't "change their spots". Does the name, Jim Nabors ring a bell?

I once had a music teacher who, as a part of his thesis, created an a cappella choir made up of people who thought they could not carry a tune. At the end of a semester, the choir put on an admirable performance. Oh, and the music teacher got an "A" on his thesis.

This is why I believe that if it doesn't make a chicken cry, it is a good voice.