interval
C perfect fourth
ClowerFupperP45 half steps
Five half steps. Turned upside down it becomes a perfect fifth.
On the keyboard
What is true of it
C up a perfect fourth is F: 5 half steps, and 4 letters counting both ends.
Turn it upside down — put the C on top — and it becomes a perfect fifth. The two numbers always add to nine, and the two sizes to twelve.
It is a perfect consonance.
Every interval on C
C → D♭minor second · dissonanceC → Dmajor second · dissonanceC → E♭minor third · imperfect consonanceC → Emajor third · imperfect consonanceC → F♯augmented fourth · dissonanceC → G♭diminished fifth · dissonanceC → Gperfect fifth · perfect consonanceC → A♭minor sixth · imperfect consonanceC → Amajor sixth · imperfect consonanceC → B♭minor seventh · dissonanceC → Bmajor seventh · dissonance