The Mystery of 7th Chords

Last Updated on February 19th, 2020


At some point during our musical education, we come across the confusing idea of 7th chords. Major 7? Minor 7? Diminished 7? And just plain ol’ 7? Aren’t they the same? And who cares! I just play power chords anyway! True, if you just play power chords and intend to keep doing that for the rest of your musical life, the idea of 7th chords probably won’t matter. But just in case we want our harmonic vocabulary to grow beyond root & 5th and simple major or minor triads, this article may help explain a few things.

Even this goofy guy can play many 7th chords. Can you?

I have to admit, when I was learning about harmony and working on chords in the first position on the guitar, I was very confused about this whole 7 thing. The trick is to understand not only the sound of each chord but how each chord works in a chord progression.
We’ll keep everything here in C, because the key of C itself has no sharps or flats- think of just the white keys on the piano.
The C scale has 7 notes: C D E F G A B
If we take the 1st, 3rd, & 5th note, it is a C major chord (C E G). If we add the 7th note (B) to the chord, it is a major chord with a 7. Or a Cmajor7. It’s generally used as a tonic chord in a progression- the chord something else resolves to. Listen to this chord progression and hear the 2nd to last chord resolve to the C major7 at the end:

Now if we take that 7th note of the scale and flat it by one fret, we get a C7 chord: C E G Bb. This note has tension and it really wants to resolve to something else. It’s usually used as a chord that leads back to the tonic chord in a chord progression. Chords with just a letter and a number 7 (C7, D7, F#7) with nothing in between the note name and the 7 are called dominant chords. These are chords with a certain amount of tension, that want to resolve to a major or major 7th chord a 5th lower, like a G7 to Cmajor7 chord progression.

We’ll now bring this to the minor realm. Again:
C : C D E F G A B
A C minor chord contains the 1, b3, & 5- C, Eb, G. Add the b7, and you get a minor chord with a b7, or C minor 7 (commonly written as Cm7). This is a fancier sounding minor chord, and usually any time you need a minor chord in a progression you can jazz it up by playing a minor 7th chord. So while a simple chord progression might be Dm Em G C, we can make it more interesting by adding the 7th note for each chord:
Dm7 Em7 G7 Cmaj7

Diminished Chords
These are chords that have a lot of tension in them. They feel like they need to resolve, generally back to the tonic chord of the chord progression. Yes, just like the dominant chord above- so frequently, diminished chords can function as a substitute dominant chord.
A diminished chord uses the 1, b3, and b5. Now the confusing part: if you add the b7, it isn’t called a dimished 7th chord. It is called a half-diminished 7th chord, or more commonly, a minor 7 flat 5 chord. And if you double-flat the 7: 1, b3, b5, bb7, or C, Eb, Gb, Bbb (enharmonically A), you come up with a diminished 7th chord. Both chords are dissonant, and both can resolve to a major 7th chord ½ step higher.

Here is a Cm7b5 chord resolving to a Db:

Here is a Cdim7 chord resolving to a Db:

7th chords don’t have to be confusing. Think of it this way: Dominant (C7, F7, etc) and diminished 7th chords have tension and need to resolve. Major 7th and minor 7th chords are chords that those tension-filled chords resolve to.

Of course, all rules are made to be broken, and blues and jazz are filled with people using these chords in interesting ways. You really have to experiment, and learn how songs use 7th chords so you can decide how you want to use them. Your songs will be more colorful, and more harmonically rich. After using them for a while, simple power chords and triads are not nearly as interesting! Below is an iconic example of using major 7ths in songwriting (on the word moves).

How have you used 7th chords in your playing? What are some of your favorite songs that use lots of 7th chords?

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