interval
A major seventh
AlowerG♯upperM711 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
A up a major seventh is G♯: 11 half steps, and 7 letters counting both ends.
Turn it upside down — put the A 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 A
A → B♭minor second · dissonanceA → Bmajor second · dissonanceA → Cminor third · imperfect consonanceA → C♯major third · imperfect consonanceA → Dperfect fourth · perfect consonanceA → D♯augmented fourth · dissonanceA → E♭diminished fifth · dissonanceA → Eperfect fifth · perfect consonanceA → Fminor sixth · imperfect consonanceA → F♯major sixth · imperfect consonanceA → Gminor seventh · dissonance