Major 7ths and A Wee Bit More Theory

In the earlier theory post I talked a little about triads: groups of three notes formed by taking every other note from a scale. There are four basic triads: major, minor, diminished and augmented. In the previous post I looked at making chord shapes and playing inversions based around the major triad. In later posts I’ll look at minor and diminished triads.

Major chords using just the root, major 3rd and perfect 5th can get a bit boring, especially if you are sitting on one chord for more than a bar or two. Adding in inversions can add a little movement, but it’s still harmonically quite ‘sterile’. One of the standard things to do is to play 7ths to add a bit of interest.

If we take our basic triad and then keep counting in our ‘every other note’ pattern, our chord consists of the root, 3rd [major or minor], 5th [diminished, perfect or augmented] and a 7th. There are three types of 7th interval.

Major 7th: the interval of a major 7th is 11 semi-tones, the major 7th is a semi-tone (or one fret) below the octave. With a G chord, the major 7th is F#.

Minor (or dominant) 7th: the interval of a minor 7th is 10 semi-tones, the minor 7th (or dominant 7th) is a full tone (or two frets) below the octave. With a G chord, the minor 7th is F.

Diminished (or double-flatted) 7th: if you lower the minor 7th by another semi-tone you get a note a full-tone below the major 7th. This double-flatted 7th is enharmonically the same note as the major 6th. With a G chord, the bb7 is E (or Fb).

Seventh chords are built from a triad plus a 7th. The usual 7th chords you’ll see are:

Major 7th: [maj7, M7 or Δ7] major triad + major 7th – 1 3 5 7, e.g. G B D F#

Dominant 7th: [min7 or m7] major triad + minor 7th – 1 3 5 b7, e.g. G B D F

Minor 7th: [m7 or min7 or -7] minor triad + minor 7th – 1 b3 5 b7, e.g. G Bb D F

Minor 7th flat 5: [m7b5 or ^Ø7 or -7b5] diminished triad + minor 7th – 1 b3 b5 b7, e.g. G Bb Db F

Diminished: [ °7 dim7] diminished triad + double-flatted 7th – 1 b3 b5 bb7, e.g. G Bb Db E (or Fb)

Despite what you’d expect, chords notated with a plain 7 are dominant 7ths [with the b7 or m7] not major 7ths.

In this episode, I’ll stick to illustrating some basic shapes for the major 7th chords, which you can use as an alternative to the major chord to add harmonic interest. All of these shapes could have been used as alternates to the major triads and inversions in the previous post. Note, that whether a major 7th or a dominant 7th is the appropriate expansion of a major triad depends on which scale degree the major triad is built on. In the key of G for example, G major and C major are major 7ths and D major is a dominant 7th. I’ll explain why this is in a later post. For now, here are the shapes:

G major 7th – four possible inversions

root third fifth maj7th

Just like in the previous post you can play swing versions of all of these, omitting the B string.

root third (with 7th) third (no 7th) fifth maj7th

I’ve shown two swing versions with the 3rd on the low E-string. One where the major 7th is played on the D string, and one where the root/octave is played there. The one without the major 7th is easier to play.

Note, major7ths aren’t used much in classic 1930s swing chord progressions although they are heavily used in be-bop and later jazz styles. Instead, what you’ll see used to add harmonic interest is the major chord (just the triad notes) being replaced with a major 6th chord — the major triad plus the 6th. Here are some 6th chord shapes.

root third fifth sixth

Again, all of these chords can be played as swing voicings, omitting the B string.

root third fifth sixth

You’ll notice that the swing chord shapes with the third on the bass are almost the same above — this is because that particular shape has the 6th or 7th on the B string, and it gets left off. You’ll probably also have begun to notice that some of these shapes look a lot like shapes you know by other names. This will be a subject for another post, but this interchangeability of simple shapes – G6 is the same as Em7, for example — is part of what makes playing fast chord progressions with lots of changes possible because you can play lots of chords while sitting at one fret (and not leaping about all over the fingerboard). If you had a progression that went from G7 to Em7 you could play that change by moving one finger, one fret and if it then went from Em7 to C7 you could play that by moving a different finger, one fret again.

More later. Minors, diminished and their 7ths for a future post.

~ by Matt on June 27, 2008.