Diatonic Chords and Harmony [Easy and Practical Guide]

This explanation does require a bit of theoretical knowledge. Most importantly, you need to know what a scale is and what a key is.

Assuming you know that, let’s move on!

Every song has a key: a collection of usually seven notes that it’s based on.

When a chord is diatonic, it means that it’s constructed using notes that are in that key.

And that’s the reason that diatonic chords sound like they ‘belong’ together: they all use notes that are in the key!

Let’s see how that works in practice.

Here’s are note notes in the A major scale.

A B C# D E F# G#

Now, all we need to do, is see what chords we can create from these notes.

We’ll take each note, and build a chord ‘on top of it’.

As you might know, a triad (three-note chord) normally consists of a third and a fifth.

So, for A we’ll add a C# and an E. That gets us an A major chord.

For B, we’ll add a D and an F#, which gets us a B minor chord.

When we keep going like this, we get the following chords:

So, these are all the diatonic chords (triads) in A major!

Now, how is this useful? That’s what we’ll see in the next section.

For example, say you’re playing along to a song in the key of D major.

It’s useful to know which chords fit in they key, or in other words, which chords are diatonic. This helps you know what to expect.

For example, it’s pretty unlikely you’ll come across an Ab major chord (though not impossible), while you’ll almost surely (highly probable) come across a G major chord or an A major chord.

This is of course also very useful when you’re figuring out chord progressions by ear. Because all the notes are taken from the key, diatonic chords have a pretty specific sound. They sound pleasing to our ears. If you can learn to recongise that sound, you know you’re dealing with diatonic chords.

Of course, some songs will also use chords with notes that are outside the key: non-diatonic chords. That’s a different sound and it usually sticks out quite dramatically. This helps you when you’re figuring out chord progressions by ear, because you know you need to look for a ‘weird’ chord.

For the same reasons, diatonic harmony is useful when writing a song. It helps you to know which chords will sound good together, but also which chords you can pick if you want something that sounds a bit different (i.e. non-diatonic chords).

In short, diatonic chords are useful in pretty much any situation that you’re dealing with chord progressions!

To recap really quick: diatonic chords are all created from the same scale. For example, when we take the notes from the A major scale, we can create the following chords:

Here’s what they sound like when we play them in order.

Sounds very neat and orderly right? Like these chords really belong together. And that’s because they’re all based on the A major scale.

Now, what’s cool is that there’s actually a hidden structure to diatonic chords. We use Roman numerals to uncover that structure. We simply give each chord its own Roman Numeral. Check it out:

So, why do we need these Roman numerals? Why can’t we just look at the chord names? The big advantage of Roman numerals is that they allow us to the logic of our diatonic chord progressions.

As an example, let me expand our chart a bit and add the Db major scale:

This chart allows us to see for example, that the D chord in A major has the same Roman numeral as the Gb chord in Db major.

Knowing that, let’s take a quick look at these two chord progressions:

A / A / D / A

Db / Db / Gb / Db

At first glance, these chords have nothing in common. But when we analyse them using Roman numerals, they actually both follow the exact same pattern!

I / I / IV / I

As you can see, they’re both a both I – IV – I progression (say “one – four – one”).

That’s what makes Roman numerals so useful. You can see the underlying structure in (diatonic) chord progressions. This not only allows you to see patterns but also makes chord progressions much easier to remember.

It’s best to give this a try yourself. Here’s a quick exercises from my course Music Theory from Scratch, where you analyse a diatonic chord progression.

This tune by the Cure is in the key of A, so that means it’s built on the A major scale. Hit play on the song so you can hear the chords. Next, see if you can find the correct Roman numeral for each chord. Refer to the table above to see what chords we can create in that scale and which Roman numeral is belongs to each chord.

Hope that went well for you! Of course, there’s much more practice like this in Music Theory from Scratch!

Let’s keep exploring and check out Minor Diatonic Chords!

Similar to major diatonic chords, minor diatonic chords are constructed using the notes from a specific scale. For example, here are the chords we can create from the natural A minor scale:

And here’s what they sound like:

Hear how that sounds completely different than our major diatonic chords? This quick example is based on a minor scale, which makes it sound sadder, darker and a bit more dramatic.

Now, as with major chords, we can use Roman numerals to reveal the structure of minor diatonic chord progressions. (For an explanation of Roman numerals, check out the last section on major diatonic chords.)

It’s best to see this in action. Let’s analyse a song by Red Hot Chili Peppers. Give the chords a listen, and then try to find the correct Roman numeral for each chord. The song is based on the A minor scale, so you can refer to the table above.

Hope you got that one! Of course, there's more of these exercises in Music Theory from Scratch!

In short, getting comfortable with diatonic chords is incredibly useful. It will deepen your understanding of music and help with a range of skills such as songwriting, improvisation and ear training.

So, what’s the next step? As with any theory: put it into practice! Take some songs you like to play and see if you can analyse them using Roman numerals. It might be tricky at first, but you’ll get quicker at it with practice. The more songs you analyze and play, the more familiar the theory will become!

As always, if you have any questions or thoughts on how this article can be better, let me know! I’m happy to help.