Determining The Key Of A Melody - Part 3 - ZERMELO

Determining The Key Of A Melody – Part 3

Today is Part 3 of the series for determining what key a melody is in — regardless of whether it's a bass line, vocal, synth loop, whatever.

Minor Scale Formula.

In PART 1, we looked at the Minor Scale Formula. And we used it to derive the notes in any minor scale.

This is important because … if you know the notes in the melody, then you can simply see whether those notes “belong” to a minor scale.

Also remember that we're ONLY looking at the minor scale for now. Melodies are written in TONS of different scales, but in house music the minor scale is the most common.

So we'll continue to look at the minor scale because it will cover the most ground for you. Later we'll look at other scales.

Scale Degree Names & Intervals.

In PART 2, we looked deeper inside the minor scale. We learned the scale degree names (in order):

Tonic, supertonic, mediant, subdominant, dominant, submediant, subtonic.

We also looked at the intervals that exist between the tonic (first scale degree) and all the other notes in the scale.

This is important because … understanding how intervals work in the scale will help you make sense of what's going on in a melody. You'll be able to see how a melody “maps” onto a scale — and that will help you determine the key.

We also saw that melodies follow 3 general shapes: up, down, and flat. Up melodies usually move AWAY from the tonic. Down melodies usually move TOWARD the tonic. And flat melodies usually dance AROUND the tonic.

In this way, melodies can “point” you to the tonic note — which will help you determine the key.

Important Notes.

In Part 3, today, we're looking at the most “important” notes and the most “interesting” intervals in scales. These are usually dead giveaways for what scale a melody is in.

The most “important” notes in the scale are the notes of the tonic chord — or the tonic chord tones.

This is a new idea, so let's flesh it out a little…

We know that the tonic NOTE is the home of the scale. And therefore, the “home” of melodies.

In a similar way…

The tonic CHORD (or the chord built from the first scale degree) is the “home” of chord progressions in a given key.

So for example, the chord A minor is the tonic chord of the key of A minor. And therefore it is the “home” of any chord progression in A minor.

Just like how melodies move away from or toward the tonic NOTE, chord progressions move away from or toward the tonic CHORD. Analyzing chord progressions is more complicated than melodies, so let's ONLY stick with the simple idea:

The tonic NOTE is the “home” of melodies. The tonic CHORD is the “home” of progressions.

The thing is melodies often highlight tonic chord tones. A melody can play the tonic chord tones a lot. Or a melody can land on tonic chord tones at key points in the melody.

So when you see a melody highlighting notes that outline a chord, chances are it's the tonic chord. And if you can identify the tonic chord, you can identify the key.

Obviously, the next task is helping you identify these “important” notes. And that means learning how to figure out the notes of the tonic chord…

How To Build Chords.

So let's talk about chords so you understand what the tonic chord is — and how it relates to the scale it's derived from.

Chords are build directly from scales. And regardless of what scale you have, chords are always built in the same way.

Remember how there are 7 notes in the scale? Let's just list the numbers:

1, 2, 3, 4, 5, 6, 7

You build basic (3-note) chords by selecting every other scale degree. Like this:

  • Chord 1 = 1 3 5
  • Chord 2 = 2 4 6
  • Chord 3 = 3 5 7
  • Chord 4 = 4 6 1 (just circle back around!)

And so on all the way up to Chord 7.

There are 7 notes in the scale, so there are 7 chords in a key because you can build a chord off each scale degree.

Example – Building Chords.

Let's build the chords of D minor:

D E F G A Bb C

  1. Tonic chord = 1 3 5 = D F A = D minor
  2. Supertonic chord = 2 4 6 = E G Bb = E diminished
  3. Mediant chord = 3 5 7 = F A C = F major
  4. Subdominant chord = 4 6 1 = G Bb D = G minor
  5. Dominant chord = 5 7 2 = A C E = A minor
  6. Submediant chord = 6 1 3 = Bb D F = Bb major
  7. Subtonic chord = 7 2 4 = C E G = C major

So 3 points here:

#1 – The MOST important thing you have to know here is HOW to build the chords. And it's clear by now that you simply build chords from the scale itself.

#2 – You might be wondering how I know whether a chord is major, minor or diminished. Don't worry about that for now — because you don't need to know this for determining the key. I just added the chord names for completeness.

#3 – I'm going to say it again: The MOST important thing is that you understand that chords are built from scales — and that you see HOW to do it.

Tonic Chord Tones.

So let's go back to the idea just before we started building chords:

Melodies will often highlight the tonic chord tones.

This statement will have a new meaning for you — it will make more sense now.

And here's the punchline:

The important notes in the scale are the tonic chord tones — with scale degrees of 1, 3, 5. These notes are often played during key moments of the melody. So if you see the melody highlighting notes that “create” a chord, chances are that chord is the tonic chord.

And if the melodic shape is ALSO “pointing” toward the tonic note, then game over! You can identify the tonic, and therefore, the key.

Here's another way to think about this:

Let's say you have a melody with D, F, A, and C.

We can use the Minor Scale Formula to map out the minor scales of D, F, A, and C to determine which of these scales the melody belongs to.

If you do this, you'll see that the melody could belong to D minor and A minor. That is, BOTH the keys of D minor and A minor have the notes D, F, A, and C.

A minor: A B C D E F G

D minor: D E F G A Bb C

So which key does the melody belong to? A minor or D Minor?

Well, we can also see that the melody outlines the tonic chord of D minor:

1 – 3 – 5 = D – F – A

It also adds the C note — which is a popular note (or “extension”) to play with the D minor chord:

1 – 3 – 5 – 7 = D – F – A – C

This chord is called a D minor 7th because you're adding in the 7th scale degree into the D minor chord.

(Side note: Jazz theory actually treats minor 7th chords as basic chords. So jazz considers D minor 7th as the tonic chord. But in “intro” music theory, a basic chord is usually a “triad” or a chord with 3 notes.)

On the other hand, what scale degrees are the notes D, F, A, and C in the key of A minor? They are (respectively): 4, 6, 1, and 3.

We can see that A and C are scale degrees 1 and 3 (respectively) of A minor. But we don't get the full tonic chord — we're missing the E note.

We also have scale degrees 4 and 6 which are a little “out of place” — especially when compared to how well the melody fits into the key of D minor.

Now, do we KNOW with 100% certainty that this melody is in D minor? Absolutely not. Because it could absolutely belong to A minor.

The only way to know is to try both D minor and A minor out.

And that's the entire point…

You've narrowed it down. And now you just have to see which sounds better.

Some Encouragement.

All this might seem like a lot of work…

After all, you've probably read about 3,000 words up until this point.

But honestly, it would take me about 3 seconds to figure out that I need to try D minor or A minor.

And remember, we're only looking at minor scales. This melody COULD work in other scales and modes too!

That's what's great about music theory. Instead of closing the doors on creativity … music theory blasts them wide open and offers possibilities your ears wouldn't have otherwise heard.

For example…

I know that D minor or A minor could work. But there's a ton of other possibilities that I could “play with” (that we haven't looked at … yet). And that's what's fun. Music theory helps me be aware of these other possibilities that my ears would never “think” of.

So not only can you identify keys extremely fast once you get the hang of it … it also opens up a world of creative possibilities for you to explore with your music.

Interesting Intervals.

The “interesting” intervals in a scale are the half-step relationships.

Let's go back to the Minor Scale Formula:


You can see that there are two half-step relationships in the minor scale:

Between scale degrees 2 and 3, and between scale degrees 5 and 6.

When you see half-step movements in a melody, you should zoom in! Because these guys are more revealing than anything!

Let me show you what I mean.

Let's compare the Minor Scale Formula with the Major Scale Formula.

(We haven't covered the Major Scale Formula, but I think you'll get it at this point.)

Minor Scale Formula: W H W W H W W

Major Scale Formula: W W H W W W H

See how the half-step relationships are in different places? Here's the big idea:

The difference between all scales and modes are WHERE the half-steps are.

That's why these guys are so revealing. Because the half-step relationships really define the key.

There's ONE more piece to “interesting” intervals:

The half-steps “like” to move in certain directions.

The 6 likes to move to the 5.

And the 2 likes to move to the 3.

Can you guess why? Hint: it has to do with the “important” notes.

As you can see, the 6 wants to go to 5 because 5 is a tonic chord tone. And 2 likes to go to 3 because 3 is a tonic chord tone.

The half-steps like to resolve to tonic chord tones.

The 6 and 2 are dissonant notes in the scale — not in bad way, but in a way that creates a colorful tension. And that tension gets released (properly) when these dissonances resolve to their stable, consonant neighbors.

Isn't that … well … interesting?

So look out for these half-step movements in melodies. They'll tell you WHERE in the scale the melody is playing — which will point you to the tonic and the key.

Example – Analyzing A Simple Melody.

Let's tie everything together with a simple example:

Imagine a melody was playing these notes in this order:

F down to E down to A

I'll admit, if you just map out the F, E, A minor scales, you'll see this melody belongs to A minor. So that's easy. But…

Here we have a “down” melody. And down melodies point us toward the tonic — remember?

So I'm suspecting that A is the tonic, and therefore, we're in the key of A minor.

Then I see that there is an E. E is an “important” note in the key of A minor because it's a tonic chord tone. Remember “important” notes (from above)?

And not only is E a tonic chord tone, it's the “dominant” note in the key of A minor. And remember, the tonic and the dominant are the two most important and stable notes in a scale.

Finally, we see the half-step movement from F to E — which is the 6 to 5 movement in a minor scale.

That seals the deal. This melody is in A minor.

I hope this little example helps you see how all this works. All the “clues” converge to a single key.

What's Next?

Now, you have most of the pieces:

  • Minor Scale Formula
  • Scale Degree Names
  • Scale Degree Intervals
  • Melodic Shapes
  • Tonic Chord Tones
  • Half-Step Intervals

In Part 4, we'll just go through a ton of examples everything to help us figure out some minor scale melodies.

In Part 5, we'll look at some other scales. And in Part 6, we'll go through even more examples.


I've put together a little quiz for you testing your ability to find the tonic chord tones and the half-step relationships.

Take the quiz →

Leave a Comment

Your email address will not be published. Required fields are marked *