Major, minor, perfect

Key idea The same interval number can have a different number of half steps, and a different colour. A major third is 4 half steps (bright); a minor third is 3 (darker). Fourths, fifths, and octaves are called perfect.

C-E and D-F are both thirds on white keys. Count half steps, though, and C-E has 4 while D-F has 3. The quality (major, minor, perfect) pins down the exact size.

Intervals from C

• Minor 2nd: 1 half step (C-D♭)
• Major 2nd: 2 half steps (C-D)
• Minor 3rd: 3 half steps (C-E♭)
• Major 3rd: 4 half steps (C-E)
• Perfect 4th: 5 half steps (C-F)
• Augmented 4th: 6 half steps (C-F♯)
• Perfect 5th: 7 half steps (C-G)
• Minor 6th: 8 half steps (C-A♭)
• Major 6th: 9 half steps (C-A)
• Minor 7th: 10 half steps (C-B♭)
• Major 7th: 11 half steps (C-B)
• Perfect octave: 12 half steps (C-C)

• Major 3rd: the start of "When the Saints Go Marching In".
• Perfect 4th: the start of "Here Comes the Bride".
• Perfect 5th: the first leap in "Twinkle Twinkle Little Star".
• Octave: the start of "Somewhere Over the Rainbow".