Which of the following is not a common musical interval used in chords?

The concept of musical intervals is fundamental to understanding chords and harmony in music. In the context of common intervals used in chords, major thirds, minor thirds, and diminished sevenths each have specific roles in chord construction and are frequently employed in harmony.

A major third consists of four semitones and is essential in constructing major chords. A minor third consists of three semitones, forming the basis for minor chords. Diminished sevenths, while more complex, are also common and used especially in jazz and classical music to create tension within compositions.

In contrast, a perfect fourth is traditionally considered an interval that provides a sense of stability but doesn't typically function as a building block for major or minor chords. While it can be used in certain contexts, such as in chord voicings or specific genres of music, it is less frequently employed as a foundational interval in standard triadic harmony compared to the others listed. Therefore, it stands out as not being a common interval used in the construction of traditional chords.