Forgive me DD, but now I'm confused.
One minute I think I've got it, then the next minute I don't! Isn't C7 the dominant 7th of the key of F (not Eb), and F# the dominant 7th of the key of B (not A)? For a minute I thought you meant leading tone of the key, but isn't the leading tone a half step away? E to F or A# to B? Or do you mean the b7 note of the key? Help!
A C7 is the
5th of the key of F, not the seventh. F# is the
5th of the Key of B, not the seventh. Yes, the leading tone IS a half-step away.
You CAN think of it that way, as long as it works for you. Dominant 7th and flat 7th are, to MY knowledge, the same thing. For example:
Key of F
F G A B C D E F
As you can see E is the 7th note in the Key of F. When you flatten it, it becomes Eb. So, when you play a F Maj 7 chord you play these notes: F A C E, but you get a Dominant 7th chord when you flatten the E: F A C Eb.
I hope that makes sense.
