Last night, I was talking with a friend of mine, and we were discussing something about chords.
I said that I did not know which chord I was using in a song that I produced lately, Vultus Solis, online on Spotify. I wanted him to make a piano line for my new unreleased song. I knew the notes that I was playing, but I did not know what the chord was.
Then I checked online and figured out that it was D minor ninth.
So I wondered:
How does it really work?
We both put our heads onto this and tried to figure it out on our own. Here is the story.
Starting with sevenths
First, we tried to figure it out by going over how sevenths work.
For example, let's take do, or C, as a note.
A C major seventh chord needs:
C, E, G, B
In solfege, that is:
do, mi, sol, ti
So what are these notes?
They are the:
1st, 3rd, 5th, and 7th
notes of the C major scale.
And if we want to go from C major seventh to C major ninth, it is actually not that hard, because C major has no accidentals. This makes the relationship very easy to see.
A C major ninth chord has the:
1st, 3rd, 5th, 7th, and 9th
notes of the scale.
So the logic is very simple:
We keep stacking notes by odd numbers.
The basic major chord
In order to clearly see this, if you have a piano in front of you, that is probably the best way to understand the core logic.
But if you do not have one, you can do what I did: just draw a little piano in a sketch.
Or you can simply write the key that you want to learn the chords about.
For example, if we are going to talk about C major, we can write the C major scale like this:
C, D, E, F, G, A, B, C
If you want to play a simple major chord, you need:
root + third + fifth
So what do we mean by third and fifth?
Once you write down the whole scale of the key, you take the notes that are in the order of:
1st, 3rd, and 5th
For C major, that means:
C, E, G
C is the first note, which we also call the root. E is the third note. G is the fifth note.
So whenever you press these notes together, you get a C major chord, without any seventh, ninth, or anything else.
We are going to build our knowledge on top of this.
From C major to C major ninth
Now let's say that we want to make C major ninth, or Cmaj9.
What this says is that we have to go until the ninth note, and we have to do this in odd numbers.
So we take the:
1st, 3rd, 5th, 7th, and 9th
notes.
In C major, that gives us:
C, E, G, B, D
- 1st = C
- 3rd = E
- 5th = G
- 7th = B
- 9th = D
That is the basic logic of a C major ninth chord.
Seeing the same logic in D major
Now let's take this onto another level and see how it works in a key with accidentals.
We can inspect the key of D major, because D major has two accidentals: F sharp and C sharp.
The D major scale is:
D, E, F#, G, A, B, C#, D
If we want to build a D major eleventh chord, we can write the scale until the eleventh note:
D, E, F#, G, A, B, C#, D, E, F#, G
Now we take the odd numbers again:
1st, 3rd, 5th, 7th, 9th, and 11th
So we get:
- 1st = D
- 3rd = F#
- 5th = A
- 7th = C#
- 9th = E
- 11th = G
So a D major eleventh chord gives us:
D, F#, A, C#, E, G
If you press these keys on the piano, you would get a D major eleventh sound.
A quick shortcut for ninths, elevenths, and thirteenths
Before testing whether we really understand the logic or not, here is a shortcut.
Since notes repeat in groups of seven, the eighth note is just the first note again, but one octave higher.
So:
9th = 2nd
11th = 4th
13th = 6th
For example, if we want to find the eleventh in D major, we do not always have to count all the way to eleven.
We can remember that:
11th = 4th
So in D major:
D, E, F#, G
The fourth note is G.
That means the eleventh is also G, just one octave higher.
This is a quick way to visualise extended chords.
Testing the logic: D major 9 sharp 11
Now let's test if we really understand the logic.
A challenging example would be:
D major 9 sharp 11
You can read this as:
D major 7 + 9 + sharp 11
Why are we breaking it down this way?
Because D major 9 gives us the core of the chord, and then we can build the sharp 11 on top of it.
So first, let's build D major 7.
We take the:
1st, 3rd, 5th, and 7th
notes of D major.
That gives us:
D, F#, A, C#
Then we add the ninth.
The ninth is the same as the second note, but one octave higher.
In D major, the second note is E.
So now we have:
D, F#, A, C#, E
The last thing we need is the sharp 11.
Normally, the eleventh note in D major is G.
But the chord says sharp 11, so we raise the eleventh by a half step.
G becomes G#.
So D major 9 sharp 11 gives us:
D, F#, A, C#, E, G#
This is the same logic again, but with one extra modification.
Bonus: Relative minor and major relationship
As a bonus, I also want to go through how the relative minor and major relationship works.
Music is full of maths, and once we understand the formulation of it, it becomes much more intuitive.
The relative minor of a major key can be found by going three half steps below the root of the major key.
So what does that mean?
If we want to find the relative minor of C major, we start from C and go three half steps down.
One half step below C is B. One half step below B is B flat. One half step below B flat is A.
So we can confidently say:
C major's relative minor is A minor.
Another way to see this is that the relative minor starts from the sixth note of the major scale.
In C major:
C, D, E, F, G, A, B, C
The sixth note is A.
So again:
C major → A minor
That is the relationship.
The notes are the same, but the emotional center changes.
C major feels like "home" when C is the root. A minor feels like "home" when A is the root.
Same notes, different gravity.
And that is one of the beautiful things about music theory: once you understand the pattern, what seemed mysterious starts to become visible.