key signature
B♭ major
B♭1C2D3E♭4F5G6A7
2 flats, written B♭ E♭
The chords that live in it
B♭degree 1 · majorCmdegree 2 · minorDmdegree 3 · minorE♭degree 4 · majorFdegree 5 · majorGmdegree 6 · minorAdimdegree 7 · diminished
Built by stacking thirds inside the scale and asking what quality comes out, rather than from a table of roman numerals.
What is true of it
B♭ major has 2 flats.
They are written in this order, always: B♭ E♭.
Its notes are B♭, C, D, E♭, F, G and A.
Relative: G minor has the same 2 flats. Parallel: B♭ minor has 5 flats, which is why changing mode changes the signature by three.
Every key
C♭ majorG♭ majorD♭ majorA♭ majorE♭ majorF majorC majorG majorD majorA majorE majorB majorF♯ majorC♯ majorA♭ minorE♭ minorB♭ minorF minorC minorG minorD minorA minorE minorB minorF♯ minorC♯ minorG♯ minorD♯ minorA♯ minor