By adding extra notes on top of the basic triads, it is possible to create various types of seventh chords. The 7th degree is either a major or minor third interval above the basic triad. The formulas for the five basic types of seventh chords are shown in the following diagram.
The final type of seventh chord is the diminished seventh. This chord is unusual in that it contains a double flattened 7th degree ( bb7). This note is actually the same as the 6th degree (A) but it is technically called Bbb7 because the interval has to be some kind of seventh rather than a sixth because the chord is a type of seventh chord.
A major 7th chord is created by adding a 7th degree to any major chord. For example, a Cmaj7 chord contains the notes C, E, G and B (1, 3, 5 and 7). The following chord diagrams demonstrate some common open major 7th chord shapes.