Fig. 1 · F to B

interval

F augmented fourth

FlowerBupperA46 half steps

A perfect fourth widened by a half step. Same sound as the diminished fifth, different letter, different behaviour.

On the keyboard

Fig. 2

What is true of it

F up a augmented fourth is B: 6 half steps, and 4 letters counting both ends.

Turn it upside down — put the F on top — and it becomes a diminished fifth. The two numbers always add to nine, and the two sizes to twelve.

It is a dissonance.

Six half steps can be written two ways: F to B is a fourth, F to C♭ is a fifth. They sound the same and behave differently.

Every interval on F

F → G♭minor second · dissonance F → Gmajor second · dissonance F → A♭minor third · imperfect consonance F → Amajor third · imperfect consonance F → B♭perfect fourth · perfect consonance F → C♭diminished fifth · dissonance F → Cperfect fifth · perfect consonance F → D♭minor sixth · imperfect consonance F → Dmajor sixth · imperfect consonance F → E♭minor seventh · dissonance F → Emajor seventh · dissonance

C A4 C♯ A4 D♭ A4 D A4 D♯ A4 E♭ A4 E A4 F♯ A4 all 204