Chord Construction – Some Music Theory Definitions

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Over the last couple of articles there have been a few things that may have raised a few questions.

When is a 2nd a 9th and Vice Versa?

The C Major Scale is as follows –

As you can see a D is both a 2nd and a 9th, so when is it which one? Normally the 9th is played an octave higher than the 2nd but occasionally different voicings are used.

A 9th chord is an extended chord so by using the term 9th it implies that there is a 7th of some sort.

9th - 1 3 5 b7 9
Maj9 - 1 3 5 7 9

Add 9 chords have the 9th added but no 7th.

Add9 - 1 3 5 9

If the term 2nd is used, it is normally used in a Sus chord and would imply that there is no 3rd.

Sus2 - 1 2 5
7sus2 - 1 2 5 b7

The same holds true for a 4th and 11th.

Normally these notes are played in ascending order, for guitarists however, it is more difficult, you can’t always play the notes in order, so naming the notes is complicated. By looking at what other notes are being played and following the ‘rules’ you can work out what to call it.

Enharmonic Spelling

Another term that gets used a lot and taken for granted is Enharmonic Spelling. This refers to a note that is identical in pitch but named differently. For example, Bb and A#. They are played in exactly the same place just called different things at different time!

Its main use is to make reading sheet music easier. A Major Scale has 7 notes, the aim is to have one note of each letter so there is one note on each staff.

C Major

The only key with no sharps or flats.

If you then look at G Major and list all the letters:


You can see that this spread doesn’t give us the correct intervals for the Major Scale (T,T,ST,T,T,T,ST). We need to play the F one semitone higher. It will, therefore, become an F# because we already have a G.

Now using F Major, following the same methodology:


Again, the intervals are incorrect. The gap between the A and B is incorrect. It should be a semitone, so the B becomes a Bb.

Normally the enharmonic equivalent notes lie between the notes that have a black key on a keyboard. But sometimes you find some oddities like E#. There is no note between E and F so E# is the enharmonic equivalent of F!

There are some scales that are Enharmonic equivalents.

For Example

F# Major
F# G# A# B C# D# E#

Gb Major
Gb Ab Bb Cb Db Eb F

Scales with double flats and double sharps do exist, but in practice they very, very rarely occur!

Last week we discussed the Dim7 chord –

1 b3 b5 bb7

In chords we can end up with a double flat note. In the case of a Cdim7 the Bb note is played one semitone lower, hence the name Bbb. Its enharmonic equivalent is A, they are played in exactly the same place, just called different things. To remain consistent and to avoid confusion it is referred to as a Bbb. Calling it an A would imply it was a 6th (yes, a 6th and bb7 are the same note!).

Hopefully this makes some sense!! Practice hard, have fun, and next week we'll take it a step further!!

-Duncan Richardson - MU Columnist

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