In my previous posts I showed how I teach basic chords (triads). Here I would like to explain how I teach seventh chords (4-note chords).
I find that many people who have come from other teachers, or who have self-taught, have a cumbersome and confusing way of trying to remember seventh chords. Many have learned a method that involves playing one type (e.g. Major 7th chord) and then altering it, note by note (e.g. lower the 7th, lower the 3rd, lower the 5th, etc.) to get the chord they want. This multi-step process is simply too slow for real-time playing. Others have used a chart which shows all the chords, triads and seventh chords, written out in notation, and have tried to memorize the notes of every chord. This would mean memorizing over 100 distinct chords, a very long process for a beginner.
Why not just learn how each type of chord is constructed? Once you know the "system," you can use it to build any chord starting on any note. It involves far less rote memorization, yet you can become quick enough at forming the chords to do it in "real-time" playing.
Before seeing how seventh chords are constructed, we have to understand intervals, specifically the meaning of "major" and "minor" as they pertain to intervals. The word "major" means big, and the word "minor" means small. They do not refer to the associations we have with them, major being the happy, bright sound, and minor being the somber, dark sound. A major 7th interval is the larger of the two possible 7ths; a minor 7th interval is the smaller of the two possible 7ths. (If the preceding description of intervals is completely new and confusing to you, you will need to get a book on theory that explains intervals.)
Every seventh chord has a triad as its base, and adds a 7th, measured from the root of the chord. If you know the construction of the major, minor, and diminished triads, and understand major vs. minor 7ths (intervals), you can build the five basic types of seventh chords.
Below you'll see the name of the chord, followed by how it is constructed, followed by an example of the symbol used in "fake books," which are books used for learning pop and jazz music, where the chords are written using symbols, not standard notation. (I'm using G as the root for our examples).
1.) Dominant 7th chord
major triad + minor 7th G7
2.) Major 7th chord
major triad + major 7th Gmaj7
3.) Minor 7th chord
minor triad + minor 7th Gm7
4.) Half-diminished 7th chord
diminished triad + minor 7th Gm7b5
5.) Diminished 7th chord
diminished triad + diminished 7th Gdim7
The last two require a bit of explanation.
For a half-diminished 7th, the symbol used most often (again using G as our example) is Gm7b5. This is because if you form a minor 7th chord, as shown above, and flat, or lower, the 5th of the chord, you get what I have shown, that is, a diminished triad with the addition of a minor 7th.
The diminished 7th chord uses a diminished 7th interval, which is a minor 7th interval made smaller by a half-step, which means it is really a major 6th! You might wonder why is isn't called a "6th chord." Although the outer interval is "enharmonically" (sounds like) a 6th, it is still functioning as a 7th, because the chord is still built of thirds, and therefore has a root, a 3rd, a 5th, and a 7th.
I recommend to my students to keep the above chart handy, and practice building all five kinds of seventh chords on all keys, at first going around the Circle of Fifths, and later just randomly. You will find that if you understand and internalize the system, you can get proficient and playing these chords, which are, of course, essential for all jazz and most pop music.