Why Are There So Many 7s in Western Sheet Music Interval Numbers? Gmaj7 and Dmin7 Explained

Have you ever noticed how frequently '7' appears in Western sheet music, especially in interval numbers? Chord symbols like Gmaj7 and Dmin7 are commonplace, but why don't we see Gm4 or Dm3 as often? This article delves into the reasons behind this phenomenon.

Understanding Triads

In music theory, a triad is a chord consisting of three notes forming the first, third, and fifth intervals from a scale. This basic structure already includes the fundamental elements necessary to form a triad, making additional numerical notation redundant. For example, a C minor triad, which we denote as Cm, does not need extra numbers because it inherently contains the root (C), third (Eb), and fifth (G).

If a composer wishes to specify these elements in a more verbose manner, they might write "Cm135." However, this is rarely done, as the standard notation "Cm" is sufficient and more widely understood.

The Role of the 3 and 4

The third interval, indicated by '3,' plays a crucial role in defining the quality of the chord—whether it is major, minor, or diminished. The fourth interval, indicated by '4,' is often omitted or modified for various musical effects. This is because the fourth interval is adjacent to the third, only a half-step away, which can create unpleasant dissonance.

When a fourth is included in a chord (e.g., D4), it introduces pitches such as D, E, F#, G, and A. This chord's sound is often described as "yucky mud" due to its dissonant nature. However, there are exceptions. For instance, the 'sus4' chord, which instructs musicians to omit the third and add the fourth, is commonly used for specific musical effects. Additionally, the major second interval (indicated by '2') is sometimes used and is colloquially called the "μ major" or "Steely Dan chord." It adds a unique edge to the music.

The Significance of the 7

The seventh interval, indicated by '7,' is the most common extension beyond the basic triad. This is due to the tertian harmony, a fundamental aspect of Western music theory, which involves stacking intervals of a third. This pattern (1-3-5-7...) creates a sense of progression and resolution in music. Beyond the seventh, ninth, eleventh, and thirteenth intervals are also relatively common, while the sixth interval (indicated by '6') appears frequently as well.

Tertian Harmony and Musical Expression

Tertian harmony, characterized by the stacking of thirds, is a cornerstone of tonal music. When we encounter a Dm3 chord, it is redundant because the third interval (3) is already implied in the notation "Dm." Similarly, the fifth interval (5) is implied by the chord name, leading some composers to write simplified notations like G5, indicating that the chord is missing its third (G, B, D).

Chords like F6 or Db-6 are common, involving the sixth interval. The second interval (2) is also frequently indicated, especially when it sounds better in a higher voicing. This interval can add a distinctive character to the chord progression, enhancing the overall harmony and texture of the music.

Conclusion

In conclusion, the prevalence of the 7 in Western sheet music is a result of the fundamental principles of tertian harmony and the way chords are constructed. The use of the 3 and 4 is often avoided due to their dissonant nature, while the 7 is commonly used to enrich the harmonic structure. Understanding these elements can greatly enhance your musical knowledge and help you appreciate the complexities of Western music notation.