So far you have studied major and minor chord construction. The dominant 7th chord is formed by adding a flattened 7th note to the major chord, i.e., I - III - V - b VII
The addition of this flattened 7th note can be easily seen when comparing the A and A7 chords:
A
A7
Construct the following dominant 7th chords:
Remember to check the sharps of flats involved in each scale when working out the notes of a chord.
The minor 7th chord is formed by adding a flattened 7th to the minor chord, giving the following formula:
The Am7 chord illustrates this:
Am
Am7
Construct the following minor 7th chords: