The 'spelling' of a 7th chord is : root – third – fifth – seventh
That is, when we add a seventh note to the basic triad (root – third – fifth), we get one of the seventh chords.
How many sevenths – note options
Root and fifth – there are only one note each. there are no two roots, two fifth notes.
But, the third note has two options – minor or major third
The seventh note also has two note options to choose from – minor seventh or major seventh
So when you form a seventh chord, fix the root, find the fifth, then there are two options for the third note, two options for the seventh note.
Total 4 possibilities of combination of notes.
The 4 possibilities are shown on the image at the top :
minor7 Root 5th m3 m7
Dominant7 Root 5th M3 m7
Major7 Root 5th M3 M7
mM7 Root 5th m3 M7
Dominant 7th is the chord we refer to when we say ' the seventh chord'. For example if you see G7, that is G dominant 7th.
Minor 7th is also written as '-7'. For example G-7 is G minor 7th
Major 7th can be written as Δ. For example FΔ is F major 7th.
Minor major 7th is the root chord of melodic minor, but we may not find it so often in pop music.
The four 7th chords for root C
Root is C. Fifth of C is G.
Minor 3rd is Eb. Major 3rd is E
Minor 7th is Bb. Major 7th is B.
Use the table above.
Substituting for the root, fifth, third and seventh positions with corresponding note for C root, we get :
C minor7 C G Eb Bb
C Dominant7 C G E Bb
C Major7 C G E B
C mM7 C G Eb B
Playing the 7th chords on the guitar
Here are the 4 seventh chords of C played on the first three frets of the guitar.
C7 (C dominant 7th)
This chord you can play the lower E too, if you choose to, because it is part of the chord notes – C E G Bb.
C minor 7th
Here both the open E strings are to be omitted because E is not a chord note in C minor – Eb is. (Cminor : C Eb G, C minor7th : C Eb G Bb)
C major 7th
C minor major 7th
Here both the open E strings are to be omitted because E is not a chord note in C minor – Eb is. (Cminor : C Eb G, C minor major7th : C Eb G B)