In order to understand the types of 7th chords, there are some other terms that must be explained. Types of 7th chords depend on the triad and 7th interval in the chord. A triad is a chord made of three notes. In a scale, there are eight notes. For the easiest examples of each of these types of 7th chords the key of ‘C’ will be used. In the ‘C’ scale, the notes are C-D-E-F-G-A-B-C. There are no flats or sharps in this scale. However, to make the different types of 7th chords some of the notes will be flatted. Flatted means that the note is taken down a 1/2-step, B to B-flat for example.
There are 6 types of 7th chords. They are major, minor, dominant, half-diminished, diminished, and minor/major. To make each of these types of 7th chords a triad is used. The triads are major, minor, and diminished. Major triads are the first, third, and fifth notes of the scale all as played for the scale. In the key of ‘C’ this triad would be C-E-G. Minor triads are the first, third, and fifth notes of the scale, but the third note is flatted. In the key of ‘C’ this would be C-E flat-G. A diminished triad has the same notes, but the third and fifth notes are flatted. This would look like C-E flat-G flat (or F sharp). These triads are in all of the types of 7th chords.
The first type of 7th chord is the Major 7th. It has no notes that are flatted in it. This type of 7th chord is made with the major triad and a major 7th. This means that the 7th note is not flatted either. The notes in this type of 7th chord would be C-E-G-B.
The dominant 7th type of 7th chord has the Major triad and the minor 7th. The only note in this chord to be flatted is the 7th. The notes in the key of ‘C’ for this type of 7th chord would be C-E-G-B flat.
This type of 7th chord is the Minor 7th. It requires the use of the Minor triad and the minor 7th. The notes would be C-E flat-G-B flat. The 7th is also flatted.
The next type of 7th chord is the half-diminished 7th. This type of 7th chord uses the diminished triad with a minor 7th. The notes for this chord, in the key of ‘C,’ would be C-E flat-G flat (F sharp)-B flat.
The fifth type of 7th chord is the diminished 7th. This chord uses the diminished triad. It also has a diminished 7th above it. That means that the 7th is flatted twice. This type of 7th chord would contain C-E flat-G flat (F sharp)-B flat flat (or A). Any note that has two flats on it means that it is dropped a whole step from the beginning note.
The final type of 7th chord is the Minor/Major 7th. This type of 7th chord has the Minor triad with a Major 7th included. The notes would be C-E flat-G-B.
The six types of 7th chords must be made using a triad and an interval of the 7th. Some of the triads do not have any notes that are flatted; some flat two of the notes. The 7th is Major if it is not flatted and minor if it is. It is diminished if it is flatted twice. Different combinations of triads and 7th make the different types of 7th chords.