interval
B♭ major seventh
B♭lowerAupperM711 half steps
Eleven half steps: a half step short of the octave, which is why it leans on it.
On the keyboard
What is true of it
B♭ up a major seventh is A: 11 half steps, and 7 letters counting both ends.
Turn it upside down — put the B♭ on top — and it becomes a minor second. The two numbers always add to nine, and the two sizes to twelve.
It is a dissonance.
Every interval on B♭
B♭ → C♭minor second · dissonanceB♭ → Cmajor second · dissonanceB♭ → D♭minor third · imperfect consonanceB♭ → Dmajor third · imperfect consonanceB♭ → E♭perfect fourth · perfect consonanceB♭ → Eaugmented fourth · dissonanceB♭ → F♭diminished fifth · dissonanceB♭ → Fperfect fifth · perfect consonanceB♭ → G♭minor sixth · imperfect consonanceB♭ → Gmajor sixth · imperfect consonanceB♭ → A♭minor seventh · dissonance