In music, constant structure refers to a chord progression using more than two chords of the same type. For example, if a chord progression involves playing an A minor seventh chord, then a C minor seventh chord, then an E minor seventh chord, it follows constant structure because all of the chords are minor sevenths. Constant structure means a pattern of the same types of chords, and the types of chords that can be used in this application are numerous. Though chords are essentially three or more notes played simultaneously, varieties of chords are many.
Types of chords that can be used for constant structure include major chords and minor chords, as well as dominant and diminished chords plus intervals, triads, and more. Though a two-note chord is technically an interval and not technically a chord, a series of similar intervals played as chords would qualify as constant structure. An example of intervals played in constant structure might include playing the root and sixth note for three or more consecutive root notes.
When reading, writing, and learning music, intervals are a means of indicating the location of notes in a chord in relation to its root. When counting intervals, the notes progress in the pattern of the chosen scale. The root, or the bottom note in the scale, is known as interval one. The next note up is interval two. The third interval is a common participant in triads, as it helps define the common major triad chord.
The terms used to describe chords help indicate the positions of its notes in relation with the root note. When a chord is a major seventh, that means that the root, the major third and the fifth are included, as well as the major seventh interval, which is the note played just before reaching the octave root of the scale. Knowing the note pattern that builds a chord can help a composer replicate the chord in a different root for a constant structure chord progression.
A minor seventh usually includes the root note, the note one half-step below the third and the fifth, which makes a minor triad, with the addition of the note one half-step below the major seventh of the scale. This is also known as a minor-minor seventh. Another chord known as a minor seventh includes the minor triad root like the minor-minor seventh, but it keeps the major seventh on top. This is known as a minor-major seventh. Use of unstable chord progressions like the fourth and seventh chords can help give a constant structure chord line a feel of tension, while resolving it to the root gives a sound feel of release or relaxation.