Basic Theory Every Songwriter Needs to Know: Part 3

Tom Slatter

Seventh Chords and How Human Biology is Like Music Theory

by Tom Slatter

How is human biology like music theory?

They both evolved, they weren’t designed.

It is absolutely clear that no-one sat down and designed the human body. Breathing apparatus confused with eating organs? Waste organs right next to our reproductive organs? A blind spot in the eye? We’re a mess, a host of systems that clearly evolved ad-hoc.

Music theory is the same. For example, the sign for a time signature of 4/4 can sometimes be what looks like a capital C. For years I couldn’t understand it. Why a C? It only made sense when one of my tutors told me it was left over from a previous system that is no longer in use.

It’s actually a semicircle, not a C. In this previous version of written notation they’d had 4 symbols to designate time signature, depending on whether the bar was divided into twos or threes, and whether the beat was divided into twos or threes. There was a circle, a semicircle and a couple of other signs as well, but only the semicircle has survived.

There is no way you could work that out, you just have to be told it.

Which brings us to Seventh Chords.

In the last article we looked at how chords are constructed. We saw that a G chord uses the first, third and fifth notes of the G major scale, G B and D.

G a B c D e f#

We said that if you add the seventh note, F# as well you get the chord G Major 7.

What I didn’t say is that while with a G major chord you cdon’t need to say ‘major’ because everyone knows ‘G chord’ means ‘G major’, with G major 7 you have to say ‘major’. You can’t call it G7, even though on the face of it that might be logical.

Why is that?

Because G7 has an F natural in it, not an F#.

When we say ‘G7′ we mean a chord with the notes G B D F, even though you don’t have an F in the G scale.

The reason for this is that for years the most important chord in western music after the ‘home’ tonic chord was the fifth chord in the scale.

In G the tonic chord is G and the fifth chord is D.

The fifth chord is so important because it has gravity – it sounds like it has to come back down to the tonic chord. Western music for centuries has been based on the tension between fifth chord and tonic chord, so much so that the fifth chord is known as the ‘dominant’ chord.

And the dominant chord was often extended to a seventh – in the key of G the fifth chord is D. If you extend that to a seventh you get the ‘D dominant 7′ chord – D F# A C.

In the key of C that same dominant 7 chord is on a G – G B D F.

As this was the most common kind of 7 chord, its name got shortened to just ’7′, hence G7 or D7.

3 Different kinds of 7 chord

A 7 chord is therefore shorthand for dominant seventh. It contains the first, the third, the fifth and the flattened seventh ie. a note two semitones (or frets, for you guitar players) below the octave.

For example:

G7 – GBDF
C7 – CEGBb

A major 7 chord contains the first, third, fifth and major seventh ie. the note one semitone (one fret) below your octave.

For example:

G major 7 – GBDF#
C Major 7 – CEGB

A minor 7 chord contains the first, minor third, fifth and flattened seventh.

For example:

G minor 7 – G Bb D F
C Minor 7 – C Eb G Bb

There are other kinds of seven chord as well, but those are the three most common.

If we were to design the system from scratch, I would call the major seven chord just ’7′ and insist on the dominant seven chords always being called ‘dominant’, but the fact is the system wasn’t designed, it evolved over centuries.

While we’re on the subject, if I had my way our method of notating rhythm would be completely different, our system of identifying time signatures would be overhauled, I wouldn’t allow transposing instruments and that ‘C’ for 4/4 time signatures? You’d never see it again.

For the comments

Are there any basic theory subjects you’d like me to cover in future articles? Have you any questions about this article? Let me know in the comments below.

Tom Slatter is a singer-songwriter, who released his steampunk themed album ‘Spinning the Compass’ in January 2010. He is also author of the www.indiesongwriter.net blog.

If you have any questions or queries, why not follow him on twitter @tomslatter

You can read…

Part 1 of this series here: You Can Harmonize Any Song With Just 3 Chords

Part 2 of this series here: What Exactly is a Chord?

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