Intro to Diatonic Chords

In this lesson my aim is to give you a very rudimentary understanding of how musicians often think of chords and chord progressions. This lesson is just a preview of these concepts. Please don’t feel lost or overwhelmed. I always like to plant the seed of a concept in your mind first and, later on, follow up on it more thoroughly.

What are Diatonic Chords?

Diatonic chords are the chords that are derived from the notes of a key.

You should think of diatonic chords as a family of chords all tied to one another by the notes of a key. They all sort of share the same gene pool.

We’ve established that each key contains seven different notes. It is possible to build a chord on each of the seven notes in every key. Each note of the key serves as a root note for a chord. Therefore each key has 7 basic diatonic chords.

Naming the Diatonic Chords with Roman Numerals

You should remember that the notes of the major scale were numbered Root (or, 1), 2, 3, 4, 5, 6, and 7. We called these scale degrees. When we discuss diatonic chords we name them with Roman numerals corresponding to the scale degree on which each chord is built.

In practice we use uppercase roman numerals to indicate major chords and lowercase to indicate minor chords. There are some other symbols sometimes added to the Roman numerals, but we’ll get to them later.

The Diatonic Chords of the Major Scale

In a major key we would number the chords I, ii, iii, IV, V, vi, and vii°. When speaking to other musicians you would call them “the one chord” or “the five chord” and so on.

For example, these would be the diatonic chords in the key of C major and in A major:

Once you have memorized these diatonic chords and another musician says to you “the verse is one-four-five in C”, you’d know the chords were C, F, and G. If they said let’s change it to the key of A, you’d know to change to A, D, and E.

Again, this is a preview of where we’re going with this. Don’t be too concerned about memorizing it all just yet or if there are some things you don’t understand. I only want you to get the concept of numbering the chords in a key.

Why Number Chords This Way?

You might be wondering why we need this system of numbering chords with Roman numerals. Why not just name the chords with their letter names? You’ll see that numbering the chords makes things much easier to understand.

Most chord progressions closely adhere to the set of 7 chords in one key. Not surprisingly, there aren’t that many different chord progressions that can result from this small group of chords. As a result, many of the same chord progressions get used over and over though they can occur in different keys.

Here’s an example of a common chord progression in the key of C. The progression goes I – V – vi – IV. The chords are C – G – Am – F. It’s very common. You may recognize it from The Beatles song Let It Be, U2's With or Without You, or countless other songs. I'm also showing you the roots to the chords on the fretboard. Notice how they are all contained in the C major scale.

Here’s the same I – V – vi – IV progression in the key of A. The numbers are the same, but now the chords are A – E – F#m – D. Compare the fretboard note pattern for A to the previous example in C. You should see the similarities.

You should be able to hear these two examples sound the same, but they also sound slightly different. The only difference is the key. Since each key has the same intervallic structure, the distances between the chords and the types of chords (major, minor, etc) are always the same.

After a while many of these progressions will start sounding familiar to you. You’ll be able to hear whether you’re on the I chord or the V chord. You might not know what key it’s in, but you’ll hear the relationships among the chords.

After that, once you understand how to play on one common chord progression well in this way, you will understand it in all of the other keys, too.

So, learning chords and progressions by their number names improves your ear and reduces your workload of learning chord progressions. I promise it will really simplify things and make you a better musician.

In Summary

Now you should have a basic idea of how musicians number chords within keys and why. In upcoming harmony lessons I'll gently ease you into learning and memorizing the diatonic chords thoroughly. They're essential and not all that difficult.

Next we’ll be looking at the most commonly used group of diatonic chords – the I, IV, and V chords.