Dominant 7th Chord Confusion: How to Count to 7

When I was first learning chords, I spent days searching for an answer to a question I couldn't phrase right.

My question was something like: When you play a "7" chord, is it 7 notes up from the tonic of the key you're in, or 7 notes up from the root of the chord? And if it's 7 from the chord root, 7 counting in what scale?

I never found a page that answered it the way I kept asking. Everything I read assumed I already knew which "7" was which. I didn't.

The confusion is real. In the world of chords, sometimes you're counting 1-2-3-4-5-6-7 based on the scale of the key you're playing in. Then other times you're counting 1-2-3-4-5-6-7 based on the letter name of the chord. Both kinds of counting matter, but they give you different information.

Scale degrees: the role a chord plays

In the key of C major, the notes of the scale are C-D-E-F-G-A-B. Each note is numbered -- those are the scale degrees. C is 1, D is 2, G is 5, and so on.

When people write chord progressions in Roman numerals, like I-IV-V, they're referring to which scale degree the chord is built on. In C major, the V chord is built on G, the 5th degree. That G chord has a special name: the "dominant" chord. It wants to resolve back to the I chord. That pull toward home is one of the foundations of Western harmony.

The dominant 7th chord -- the V7 -- sounds even more like it needs to resolve. The added note creates tension that almost demands release. You hear it constantly in blues, jazz, hymns, pop. The V7 chord is used more often than the plain V.

Building the dominant 7th chord

How do you build G7, the dominant 7th chord in the key of C?

Start with the G major triad: G-B-D. Now add the 7th. But which 7th?

You count up from G using the scale of the key where G has dominant function -- the key of C major. G-A-B-C-D-E-F. Seven steps from G, staying inside the C major scale, lands you on F.

G7 is G-B-D-F.

And there's no ambiguity about which scale to use. G is the 5th degree -- the dominant -- only in C major and C minor. No other major or minor scale has G as its dominant. So when you're building G7 as a dominant 7th chord, you're always counting in a C scale.

Here's what tripped me up: F is not in the G major scale. The G major scale has F#. If you built a G chord using only notes from the G major scale, the 7th would be F#, and you'd get Gmaj7 -- a different chord with a different sound.

But G7, the dominant 7th, uses F natural. Because G7 originates from the key of C major, where it functions as the dominant 7th, and F natural is part of that scale.

And here's something else that confused me as a beginner: the recipe doesn't change depending on what key you're playing in. G7 is always G-B-D-F. If you're playing a piece in D major and a G7 chord appears, it's still G-B-D-F. If you're playing in Ab major and a G7 appears, it's still G-B-D-F. The chord name tells you how to build it, and that's fixed.

The same chord, two perspectives

Play a G7 chord. G-B-D-F.

From one perspective, it's the V7 chord in C major -- built on the 5th scale degree, using notes that belong to the key.

From another perspective, it's a G major triad with a flatted 7th. If you compare it to the G major scale, that F is a half step lower than the F# you'd expect.

Both descriptions are true. The chord is what it is. The names describe different things about it.

Why this matters when you're learning

If you're trying to figure out what notes go in a chord by name, you can build it from the root. G7 means: G major triad, plus a minor 7th above the root. The "7" in a dominant 7th chord is always a minor 7th interval -- a half step lower than the major 7th.

If you're trying to understand why a chord progression sounds the way it does, you think about function. The V7 chord creates tension. The I chord releases it. G7 wants to go to C.

When someone asks "why does G7 have F when F isn't in the G major scale" -- the answer is that G7 is native to the key of C, not the key of G. The dominant 7th chord is built from the scale of its home key, not from the scale of its root note.

Another example

In the key of Bb major, the dominant chord is F. The notes of the Bb major scale are Bb-C-D-Eb-F-G-A.

To build F7, start with the F major triad (F-A-C) and add the 7th by counting up from F in the Bb major scale: F-G-A-Bb-C-D-Eb. The 7th is Eb.

F7 is F-A-C-Eb.

Eb is not in the F major scale -- the F major scale has E natural. But F7 originates from the key of Bb, where it functions as the dominant 7th.

Same as with G7, the spelling doesn't change depending on what key you're playing in. F7 is always F-A-C-Eb. If you're playing a piece in D major and an F7 chord shows up, it's still F-A-C-Eb. The chord name is the recipe.

I wish I'd found a page that explained this when I was first working through it. I remember sitting at the piano trying different things until I could hear the difference. It took longer than it needed to.