I am wondering why Amazing Grace written with a G Major key signature when there is not an F/F# in the song? Since there are no sharps or flats in the song, why is this not just called the key of C? It it because of the tonic? Did I answer my own question? Seems funny to play to a song in some key without fingering any sharps or flat from that key but I guess it can be true?
That is a good and fair question John.
The answer is that it doesn’t matter if there is or isn’t an F in the melody.
The composer wrote a beautiful melody in the key of G major but found no use or need for the F note.
This is irrelevent as to the key in which the song is in. In this case it is indeed in the key of G major.
Not having an F in a piece of music that’s in G is more unusual than having one but it is indeed the case here.
If you want to analyze this music take a look at the notes used: more than any others, the most used notes in that song are G, B, and D.
when you lay out a G major chord what are the notes? G, B, D
and that is why you can’t just say it’s in the key of C.