First let's look at which scales contain B# (that aren't unreasonably daft like for example D# Major):

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. This is a really fun if slightly useless question. While it is technically possible to raise the fourth degree of a scale by 2 notes, there are few, if any circumstances where you would want to do this, and so you are unlikely to ever encounter a B♯ in F major. It would be like seeing an F♯ sharp augmented (F♯ A♯ C ) in the key of G. Quite why you would find this in a piece in F major though, I can't see. Why would you do this when you could write it as D flat major, and have a C♮?Īn E augmented chord has a raised fifth, not a flat sixth, so would be written as E G♯ B♯ (not E G# C). (this would be like borrowing from G♯ minor in the key of C major)īorrowing from C♯ major. This would be very unlikely in the key of F. Why would we ever use these spellings?īorrowing from C♯ minor, minor scales can have a sharp 7. Which way we write a given note (for example B♭ or A♯) is called a 'spelling'. You are raising the 4th degree of the scale by 2 semitones to give you an analogy, all of the following are equivalent: The important question though is would this ever happen? And the answer is rarely if ever. So for the that bar, all written B's would be played as Cs, effectively. The answer is that, yes, a B# in F major would be the same enharmonic note as a C natural. It seems like you're asking whether the sharp 'sharpens' a B flat to a B natural, or actually makes a B sharp.

F major scale b flat major scale