Fig. 1 · A# to C##

interval

A♯ major third

A♯lowerC𝄪upperM34 half steps

Four half steps. The interval that makes a triad major.

On the keyboard

C𝄪A#
Fig. 2

What is true of it

A♯ up a major third is C𝄪: 4 half steps, and 3 letters counting both ends.

Turn it upside down — put the A♯ on top — and it becomes a minor sixth. The two numbers always add to nine, and the two sizes to twelve.

It is a imperfect consonance.

Every interval on A♯

A♯ → Bminor second · dissonanceA♯ → B♯major second · dissonanceA♯ → C♯minor third · imperfect consonanceA♯ → D♯perfect fourth · perfect consonanceA♯ → D𝄪augmented fourth · dissonanceA♯ → Ediminished fifth · dissonanceA♯ → E♯perfect fifth · perfect consonanceA♯ → F♯minor sixth · imperfect consonanceA♯ → F𝄪major sixth · imperfect consonanceA♯ → G♯minor seventh · dissonanceA♯ → G𝄪major seventh · dissonance

C M3C♯ M3D♭ M3D M3D♯ M3E♭ M3E M3F M3all 204