This is a really fun if slightly useless question. Let's consider inder what REASONABLE circumstances a B# would appear in a piece starting off (because thats the ONLY thing a key signature means) in F Major. First let's look at which scales contain B# (that aren't unreasonably daft like for example D# Major):
that's it for majors
and then non-daft Minor scales:
C# Minor Let's say Melodic
D# Minor Melodic
A# Minor ?
Now let's hunt for some (but not all) USEFUL chords properly containing B# when written correctly in the key:
(You know what, to hell with A# Minor.)
C# Major = C#Ma7 E#m7 G#7 B#m7b5 (=D#m6)
C# Minor Melodic = B# ALT, F#7b5
D# Minor Melodic = B#m7 b5
Can some of them be ruled out ? I would say so! E#m7 C#Ma7, B#m7b5, B# ALT, and B#7 b5 are revoltingly preposterous from a publishing point of view, even IF you are Charlie Parker.
But, HELLO! that leaves G#7 and you would probably spell that properly.
There you go! Now we'll just figure out a pretty progression and ...
F Ma7 | F Ma7 b5 | A Ma7 | G# Ma7 b5 | G Sus Ma7 | F# Ma7 b5 | F Ma7 |
Yeah, ok so I changed it. And I know G# Ma7 b5 is in D# Major after all. Daft key. Play all these in Root inversion. Here's how it works. You're not going to spell the A Ma7 with an A Flat are you, so you're going to spell the next chord properly, G#, B#, D, FX. After that the B# is PEDALLED thru all the chords, SO YOU CAN'T CHANGE IT, even the final FMa7 ends up being spelled with a B#! If I ever figure out how to score it on a staff on this site, I will. Till then use your imaginations.
So, I don't know what was the question? Oh yeah IF you ever saw a B# it might be in a progression somefink like the one above.