Welcome to The Circle, our voyage into the mysteries of The Circle of 5ths. In this post we’ll see how geometric shapes combined with the circle can create popular chords. Let’s overlay a Scalene Triangle on the circle.
The Tension & Resolution element of the Dominant 7th Chord occurs when two notes in the chord do not get along very well together. Let’s use the D Major chord for this example. The notes in a D Major chord are D-F#-A.
When we add in the flat 7th note of the D Scale which is C, this sets up a tension between the 3rd note of the scale (F#) and the flat 7th (C). The reason for this tension is F# and C are separated by the interval of the Tri-Tone, or three whole tones. You could also look at the Tri-Tone as a half-octave interval since the distance from C to F# and F# to C is the same, three whole tones.
Notice on the circle that C and F# are separated by 180 degrees, the farthest apart that two points can be on a circle. Add in the root of the chord, D and you have the essence of the D7th chord.To break this tension, the two Tri-Tone notes need to resolve one-half step each, C to B and F# to G. The result, the D7 resolves to G Major (G-B-D). Notice also the resulting geometric shape is also a scalene triangle, albeit a smaller one.
Observation: Any two notes 180 degrees opposed to each other on the circle will create a Tri-Tone interval.