In the diatonic scale of C major the intervals from C to F, D to G, E to A, G to C, A to D and B to E are perfect fourths, each consisting of two whole steps or tones and one half step or semitone.

• 在大C自然音阶， C到 F, D 到G, E到A, G 到C, A 到 D ，B 到 E为纯四 度，每组包含两个全音或半音。F 到 B,包含三个全音，构成增四度，被称作三全音。