b flat

[henrikhank]

Pax!
When composers want to compose a song in both b flat major and minor. How do they do? What did the great composers do?

[andreslr6]

They use alterations?? 

Take a look on bitonality, here's a quick read https://en.wikipedia.org/wiki/Polytonality

Ligeti wrote music for piano where one pentagram was in one key signature and the other on another, and so did many composers. Earlier, Prokofiev and Bartok used bitonality as well, for example Prokofiev on the 1st mov of the 7th sonata, chords like A-C#-F#-A# (F# major/minor) and D-F-Bb-Db (Bb major/minor) etc.