The song "Misty Moisty Morning" by Steeleye Span is in a major
key. My knowledge of music theory is fragmentary so I may have
gotten it wrong but I believe it's true. I don't remember which
key it is originally, but I like to play it in G. In this key,
the song uses all sounds in G major, except the sound C. (So all
of these sounds are in D major too but the song ends in a strong
G sound, so I think it makes it a G major). All sounds in the
song are from G major too, except one: F, which ends the second
line of every stanza (stanzas have four lines each). My question
is: why is it OK to use this sound and it still sounds right? I
understand that this is possibly an open-ended question, so a
more specific one is this: is there a name for such a usage of a
sound from outside the scale? The song is here although the
quality is rather bad. The first occurence of this F is about
0:48, when she sings "leather". I'm very sorry if what I'm
saying is difficult to understand. Please point out any mistakes
or vague part