There are FOUR basic types of seventh chords: Major 7, Minor 7, Dominant 7 and Diminished 7. This article explains the construction and function of Major 7 and minor 7 chords.
Major 7th Chords
Formula: 1 3 5 7– This means that you use the 1st, 3rd, 5th, and 7th notes of the major scale. (EXAMPLE: C E G B) (NOTATION: CM7 or Cmaj7) This is NOT the chord you play when someone says “C7”. That is a whole different animal. Basically, this chord is constructed by starting the MAJOR TRIAD and adding the SEVENTH note in the scale.
Function: The chord-functions of the major seventh chord are two: It can function as a I chord or tonic chord built on the root of the current key. It may also function as a IV chord (also called the sub-dominant. The IV chord is used to provide a temporary “resting point” and tends to want to go back to the I chord.
To fully understand chord functions, you need to be familiar with diatonic chord progressions and key signatures. I will later give you an excellent source of information about both chord progressions and key signatures.
For example, in the key of C Major, the I chord would be C Major 7(C E G B) and the IV chord would be F Major 7 (F A C E). What about the key of G? The I chord is G Major 7 (G B D F#) and the IV chord is C Major 7(C E G B)
Minor Seventh Chords
Formula: 1 b3 5 b7 — This means that you use the 1st, flatted 3rd, 5th, and flatted 7th notes in the major scale. (EXAMPLE: C Eb G Bb) (NOTATION: Cm7 or C mi 7).
Let’s try another one–how about Eb minor 7? Did you say Eb Gb Bb Db? Then you are exactly right!
Function: This chord functions as a ii, a iii, or a vi chord. These three chords all have a tendency to want to go to a chord a FOURTH HIGHER. For example, in the key of C, “Dm7” (ii chord) would go up a fourth to “G7” (V chord) which then would go back to “C” (I chord). This well-known chord progression is called a”ii V I” progression. In the key of G major, the iii chord, Bm7 would want to go up a 4th to Em7–the vi chord, which then want to go up a 4th to Am7, –the ii chord, which in turn would tend to go up a 4th to D7–the V chord, which would then go back to G, the I chord and we would have a “iii vi ii V I” progression. Are you starting to get the picture?
