How to Harmonize a Melody: Start With Just Three Chords
One of the most intimidating parts of composing is not necessarily coming up with a melody. It is deciding what should go underneath it.
You may have a melody you like, but then face an enormous question:
Which chords should I use?
There could seemingly be dozens of possibilities. Major chords, minor chords, seventh chords, inversions, secondary dominants, chromatic chords—the choices quickly become overwhelming.
But you don't need to begin with all of them.
A remarkably large amount of tonal music can be understood—and composed—using just three chords:
I, IV and V.
These are known as the primary chords.
In a recent composition workshop, we explored how these three chords can give a composer a practical framework for harmonizing melodies without becoming overwhelmed by possibilities. compose in 4 weeks 2026-10-04 …
What Are the Primary Chords?
The primary chords are triads built on the first, fourth and fifth degrees of a scale.
For example, in C major:
I = C major
C–E–G
IV = F major
F–A–C
V = G major
G–B–D
Here's something fascinating about those three chords.
Combine all their notes:
C–E–G
F–A–C
G–B–D
Now rearrange them into stepwise order:
C–D–E–F–G–A–B
Between them, the three primary chords contain every note of the major scale.
This is one reason they are such a useful starting point for harmonization: every diatonic melody note can potentially belong to at least one of these chords. This was a principle I encountered in Tchaikovsky's approach to harmony and discussed in the workshop. compose in 4 weeks 2026-10-04 …
Why Limiting Your Choices Can Make You More Creative
When beginning to compose, more options aren't always better.
Suppose you have written a melody note and believe there are twenty possible chords underneath it. You now have twenty decisions to evaluate.
Instead, ask:
Does this melody note belong to I, IV or V?
Suddenly you may only have one or two obvious possibilities.
Try them.
Listen.
Choose one.
Move on.
This matters because composition requires decision-making. At some point, you have to decide that an idea is good enough to continue developing.
Your musical imagination may even be ahead of your current ability to realise what you're hearing. That's normal in the creative process. The solution isn't necessarily to learn another fifty chords before writing anything. A limited harmonic vocabulary can actually help you turn your ideas into finished music. compose in 4 weeks 2026-10-04 …
A Simple Method for Harmonizing a Melody
Let's say you have a melody in C major.
Your first three harmonic options are:
C major — I
F major — IV
G major — V
Take the first important melody note and ask which of those chords contains it.
If the melody note is E, C major contains E, so I is an obvious possibility.
If the note is A, F major contains A, so IV becomes a possibility.
If the note is B, G major contains B, making V a natural choice.
Some notes belong to more than one primary chord. That's where things become interesting.
You don't necessarily have a single "correct" harmonization.
You have choices.
Two different chords can support exactly the same melody note while producing different bass movement, tension and musical direction. In the workshop, we explored precisely this process: finding chords containing the melody note, trying different voicings, listening to the alternatives and choosing the solution that best suits the piece. compose in 4 weeks 2026-10-04 …
Don't Forget the Guitar
For guitarists, there is another important consideration.
Knowing that you want a C major chord isn't quite enough.
Which C major?
The guitar gives us multiple voicings of the same harmony across the fretboard. And when harmonizing a melody, we often need a particular melody note to remain at the top of the chord.
So the process becomes:
Melody note → possible chord → suitable guitar voicing
This is one of the reasons I developed the Harmonise a Note feature in Harmony Explorer. You can choose a melody note and explore chord voicings capable of supporting it, rather than having to find every possibility manually. In the workshop, we compared this with a traditional chord reference and noted the advantage of being able to hear and compare multiple voicings.
Try It Yourself with Harmony Explorer
Choose a key below and explore its primary chords. You can also use Harmonise a Note to enter a melody note and discover different chords and guitar voicings that can support it.
Learn to See the Chords Hidden Inside Guitar Music
This approach is useful for more than composition.
It can transform the way you analyse repertoire.
Classical guitar music often disguises simple harmony through texture. Instead of seeing a block chord, we might encounter:
a bass note,
several arpeggiated inner notes,
and a melody above them.
On the page, it can look complicated.
One useful analytical technique is to compress or "chunk" the notes together.
Imagine all the notes sounding simultaneously rather than one after another.
An elaborate arpeggio may suddenly reveal itself as simply:
I – V – I – V
In the workshop, we applied this to a Mertz example. Once the arpeggiated notes were stacked vertically, the underlying harmony became much easier to recognise. compose in 4 weeks 2026-10-04 …
This is an important lesson for guitarists:
Complex texture does not necessarily mean complex harmony.
A piece can sound rich and sophisticated while being built upon an extremely simple harmonic skeleton.
I and V: One of Music's Most Important Relationships
Although I, IV and V form our primary-chord family, I and V are particularly important.
I gives us stability: home.
V creates tension and points us toward I.
This movement between stability and tension is one of the basic engines of tonal music.
But V has another powerful ability.
It can lead us somewhere new.
The Dominant Is Also a Doorway to Another Key
Suppose you're composing in C major but want to move temporarily to E minor.
One of the clearest ways to establish E minor is to introduce its dominant chord and then resolve it to E minor.
In other words, you temporarily start thinking about the primary chords of your new key.
This came up naturally while analysing a Tárrega prelude in the workshop. Much of the piece could be understood through primary harmony, but Tárrega then used dominants belonging to other keys to create brief departures. compose in 4 weeks 2026-10-04 …
This creates one of the most effective expressive tools available to a composer:
change the key, and you can change the mood.
A bright major passage might suddenly move into a darker minor region.
A minor piece might briefly emerge into major.
And you don't need a hundred measures to do it. Even a very short piece can contain a small harmonic journey.
Start Simple, Then Expand
None of this means that every piece should consist exclusively of I, IV and V.
Far from it.
Eventually we can introduce:
secondary chords,
seventh chords,
inversions,
suspensions,
secondary dominants,
chromatic alterations,
substitutions,
and increasingly adventurous harmony.
But there is enormous value in understanding the skeleton before decorating it.
If you can take a melody and create a convincing harmonization with I, IV and V, you've learned something far more useful than memorising a collection of sophisticated chord names.
You've begun to understand how melody and harmony interact.
Try This Composition Exercise
Take a short melody of around four to eight measures.
First, identify its key.
Then write down the three primary chords:
I – IV – V
For each important melody note, determine which of those chords contains it. If more than one chord works, try both.
Listen to the difference.
Pay particular attention to the bass line created by your choices. Don't simply ask whether a chord is theoretically possible—ask whether the succession of chords sounds convincing.
Once you've created a simple harmonization, play it.
Then—and only then—try replacing one or two chords with something more colourful.
This gives you a fascinating comparison:
What did the more advanced harmony actually add?
That's a much better way to learn harmony than adding complexity simply because you can.
Harmony Is Something You Can Explore
Harmony doesn't have to remain an abstract theory subject.
You can hear it.
Play it.
Analyse it.
Change it.
And compose with it.
In fact, one of the simplest ways to begin spontaneous composition on the guitar is to combine these ideas: improvise with notes from a scale, recognise the harmony you're implying, add an appropriate bass note, move to another chord, and continue exploring. That begins to blur the line between practising scales, improvising, understanding harmony and composing music. compose in 4 weeks 2026-10-04 …
And perhaps that's the most important point.
You don't need to understand every possible chord before you can compose.
Sometimes creativity begins by reducing the possibilities.
Start with three chords. Make some decisions. Listen carefully. And create something.