In this blog post, I’ll provide a simple overview of diatonic chords and the basic concepts of intervals, harmonies, and chords needed to understand them.
Intervals: The Distance Between Sounds
An interval is a unit that represents the distance between two sounds. To make the explanation easier, I’ll use C (Do) as the reference note. The names commonly used in music are A, B, C, D, E, F, and G. The same note C and the C one octave higher are called an octave; C and D are a second; C and E are a third; C and F are a fourth; and C and G are a fifth.
Intervals are classified based on their character. The 1st (Do), 4th (Fa), 5th (Sol), and octave (8th) are called “perfect” and have the quality of blending harmoniously and stably when sounded together. In contrast, the 2nd (Re), 3rd (Mi), 6th (La), and 7th (Si) belong to the “major” family; they have a relatively bright sound but do not blend together as seamlessly as the perfect intervals.
Modern music uses a total of 12 notes: in addition to the basic seven notes (Do, Re, Mi, Fa, Sol, La, Si), there are chromatic notes such as Do#, Re#, Fa#, Sol#, and La#. The symbol “#” indicates a note that is a semitone higher than the original note. In the “perfect” scale, a note a semitone narrower than the perfect interval is denoted as “diminished (diminished interval),” and a note a semitone wider is denoted as “augmented (augmented interval).” In the case of major intervals, if the interval is narrowed by a semitone, it is classified as “minor”; if it is widened by a semitone, it is classified as “augmented.” For example, F# is a semitone lower than G (perfect fifth), so it can be considered a “minor fifth”; D# is a semitone lower than E (major third), so it can be described as a “minor third,” and since it is a semitone higher than D, it can also be described as an “augmented second.”
Basics of Chords
A chord is the sound produced when notes with specific interval relationships are played simultaneously. In music, multiple notes often overlap rather than a single note being played alone, and these chords play a crucial role in determining the mood of a piece.
The most basic chords are major chords and minor chords. A major chord consists of three notes—a perfect unison (root), a major third, and a perfect fifth—and conveys a bright, stable feeling. In contrast, a minor chord consists of a perfect unison, a minor third, and a perfect fifth, and conveys a darker feeling. For example, C major is C–E–G, while C minor is C–D#–G, written as Cm. The key point is that the atmosphere changes significantly simply due to the difference between the major third and the minor third.
If you add one more note to form a seventh chord, you get various tonal colors such as Major 7, 7 (dominant 7), and Minor 7. A Major 7 chord is a major chord with a major seventh added, and a 7 chord is a major chord with a minor seventh added. For example, D Major7 is D–F#–A–C# (D F# A C#), D7 is D–F#–A–C (D F# A C), and Dm7 is D–F–A–C (D F A C). Once you understand what a major third is (e.g., the major third of D is F#), these extensions will come naturally.
Why Diatonic Chords Are the Backbone of a Song
Diatonic chords are the seven triads that blend naturally within a single key. For example, starting with C Major (C D E F G A B), stacking thirds within an octave yields seven distinct chords. These seven chords are the diatonic chords, and they serve as the “pillars” that form the basic framework of many songs.
You can fully compose and analyze a song using just these seven chords because the constituent notes are consistent within the same key, resulting in minimal dissonance and natural transitions. It is usually helpful to divide these chords into three groups based on their functions: Chords 1 (tonic), 3, and 6 are considered the stabilizing group; chords 2 and 4 are seen as neutral or transitional; and chord 5 is viewed as the group that creates instability and tension. Chord 7 (typically a diminished chord) creates a strong sense of unease and is therefore not often used on its own.
In actual song composition, these groups are used functionally. The intro often uses the No. 1 and No. 2 groups to create a sense of stability and gentle movement, while the pre-chorus (just before the chorus) mixes unstable chords like No. 5 with the No. 2 group to heighten tension and build excitement. Since the chorus is the climax of the song, Groups 1, 2, and 3 are appropriately mixed to make the melody and harmony stand out.
Even if it initially sounds complex with many overlapping notes, once you understand diatonic chords, you’ll begin to see the repeating patterns and their functions. By analyzing which chord set a chord belongs to, you can explain why some sections sound stable while others sound tense. Since composition also builds upon diatonic harmony by adding various variations and ornamentations, understanding this foundation first will make it much easier to grasp more advanced harmony.
