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First of all, what even is a seventh chord?
A seventh chord is when you take a triad (made by stacking notes on top of each other in thirds) and add an extra third on top, like this:
Not all sevenths are the same, and not all seventh chords have the same function.
Seventh chords are absolutely fantastic for creating a harmonic progression with nuance and heart — sticking to just major and minor chords is like trying to build a rocket ship out of all square legos. It’ll do the job for a while, but eventually we outgrow them and want the cool wing bits and some lights and stuff. Anyway, sevenths…
What Ingredients Will I Need?
Let’s start by talking about triads. You’ve got four kinds of triads: major, minor, diminished, and augmented. Here they all are:
- A major triad is a major third with a minor third stacked on top.
- A minor triad is a minor third with a major third stacked on top.
- A diminished triad is two minor thirds stacked on top of each other.
- And an augmented triad is two major thirds stacked on top of each other.
Got it? Great. Hold onto that thought.
Now, let’s talk about seventh intervals. Just like triads, you can have four kinds of sevenths: major, minor, diminished, and augmented. Think of a seventh chord as being a combination of a triad and one of these seventh intervals.
Build Your Own Seventh!
First up — forget about the augmented triads and sevenths. Except in some weird harmonic circumstances you’re probably not going to make seventh chords with either of these ingredients.
That leaves us with major, minor, and diminished triads and sevenths. While you can combine these triads and sevenths in any combo and end up with some kind of seventh chord, there are three very common ones and two less common, yet still useful, seventh chords that we’re going to focus on today.
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The Major Seventh
The major seventh is made up of a major triad and a major seventh. If you’re playing in a major scale, the major seventh exists naturally on the I chord and the IV chord; if in minor, it’s on the ♭III and ♭VII chord. Most commonly though, it’s used on the I in a major scale, and is usually used to give the tonic chord a dissonant edge, making home feel a little more bittersweet. In chord symbols, it’s written as either M7, Maj7, or with a triangle like this: △7
The Minor Seventh
The minor seventh is a minor triad and a minor seventh. In major scales, it naturally occurs on the II–, III–, and VI– chord, and in minor scales on VI– and V– (when you don’t raise the seventh degree of the scale to create the major dominant chord, V7). Most commonly, it’s used on the II– in a major scale or the IV– in a minor scale, and is what we call a pre-dominant chord — a chord we use before the dominant. It’s written as either m7, min7, or –7.
The Dominant Seventh
This seventh is probably what most people think of when they’re talking about seventh chords. The dominant seventh is made with a major triad and a minor seventh, and is so called because it naturally exists on the V of a major scale — which is the dominant chord of the scale. It is very active and wants to return to I.
Why is it so active? Because the interval between the 3rd and the 7th creates a diminished 5th, a very unstable, dissonant interval that practically begs to be resolved inwards, to notes which just happen to be the 1st and 3rd degree of the tonic chord. Use this chord to create a strong V to I feel. You write it with just a straightforward 7 after the root note.
These three chords make up the very basic II– V I progression that is a cornerstone of western harmony. Any jazz student will learn this basic progression in all 12 chromatic transpositions, and it’s probably not a bad idea for musicians of any style to give it a go, too.
The Half-Diminished Seventh, or Minor 7 with a Flat 5
This usefully melancholic chord is one of my favorites. It’s made from a diminished triad with a minor seventh stacked on top, hence its other name, minor 7♭5, with the “♭5” describing the flatted fifth interval appearing in the triad. Shorthand, you write it out with min7♭5, or else with a little circle with a slash through it and a 7, like so: ø7.
It occurs naturally in the minor scale on the II°, and so is often used in place of a minor seventh chord in minor IIø7 V7 I– chord progressions. But it’s also extremely versatile. Because it’s so active, you can use it to easily modulate to a new key, no matter how unrelated it is to the current key you’re in.
Try it out. Fool around in your home key, land back on your tonic, then pick a random new key and go, IIø7 V7 I. I guarantee it’ll sound as smooth as a shaved billiard ball.
The Fully Diminished Seventh
The fully diminished seventh is made up of a diminished triad with a diminished seventh stacked on top, hence the name, “fully diminished seventh.” The shorthand for this chord is dim7, or with a small circle like so: o7.
Diminished sevenths sound very blue, because they’re made up of minor thirds stacked on top of each other. They’re weird chords, though, because depending on the context they’re in, they can sound either active or static. You can use them in place of a II– chord in a minor progression, or to quickly modulate to a random new chord (they’re really active because they consist of two diminished fifths which can resolve to a number of other chords).
Or, if you’re a 1920s Vaudeville villain, like me, and you’ve just tied someone to a railway track, you can move down chromatically with diminished seventh chords so everyone knows you’re the bad guy.
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