Seventh chords are extensions of the basic triad, and they provide some interesting sounds and variety to normal major/minor progressions. Major and minor chords are like primary colors. Mixing them up gives us other colors, sounds, emotions, and infuses our "normal" music with something special.
How does learning about 7th chords help soloing? Maybe it doesn't - directly - but like any other aspect of music theory, it's really helpful to understand the "why". As you start to hear things you've never heard before, you will learn to solo in response to your knowledge.
By now, you should know that a basic triad is made of 3 notes. If we are playing a C major chord, those notes are C, E, and G. Another way of labeling these notes is 1, 3, and 5 since we skip notes in the scale.
If a major chord is 1 3 5, we can also write the other kinds of triads like this to *compare* them to a major chord. The notes in a C minor triad (using the correct number of frets between the notes) turns out to be C Eb G. So when using numbers here, we could say that a minor chord is 1 b3 5 compared to the major 1 3 5. This chart compares all the triad types in this way:
| Major: | 1 3 5 |
| Minor: | 1 b3 5 |
| Diminished: | 1 b3 b5 |
| Augmented: | 1 3 #5 |
So to build a C diminished chord, you just take your major C E G and flat the E and G. This is just another way of looking at triads.
I put you through that because I'm going to write out seventh chords in the same way so you can see how they compare to each other. Here's the list:
| Major 7 (∆7): | 1 3 5 7 | C E G B | Mellow, Calm |
| Dominant 7 (7): | 1 3 5 b7 | C E G Bb | Happy, Silly |
| Minor 7 (m7): | 1 b3 5 b7 | C Eb G Bb | Mellow, Groovy |
| Half-Diminished 7 (Ø7): | 1 b3 b5 b7 | C Eb Gb Bb | Frightening? |
| Diminished 7 (°7): | 1 b3 b5 bb7 | C Eb Gb Bbb | Angry, Suspenseful |
That's not a typo, that really is a double flat (bb). You just lower the note two frets. Yes, there's a double sharp too. It looks like an "x".
The last column is how the chord typically sounds. At least, that's how they sound to my ears. Maybe you will find a different word that fits better.
If you can find notes on the guitar decently, try starting with a basic C major barre chord like this:
Then see if you can make all those sevenths just by flatting a note here and there.
There are a couple of other types of seventh chord I didn't cover here, but these are by far the most common.
In the next theory lesson we'll discover how these chords fit into a major key so you can start writing songs and progressions using these chords. And in this lesson I'll show you how to play them all over the fretboard.