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Understanding Harmony: Part 1


What is harmony? How do chords relate to one another? How can a chord progression build a framework for a song? In this tutorial we'll answer those questions by looking at the basic chords of a key.

Melody is the most important part of the music. It is the tune of the song. But harmony can add so much depth and meaning! It is the interplay of tones or chords that accompany the melody.

How does harmony give weight and depth to a song melody exactly? Each chord has its own ‘colour’ or perspective, and often seems to also have a direction of travel. It takes you to the next point in the song, either with a feeling of inevitability, or alternatively with a sense of sudden unexpected shock!

Some have likened this journey of tension, climax and release to crossing a bridge. The road arches away from the foundation of the shoreline on one side (the home key at the beginning of the song), and takes you through a varied journey of discovery, before returning you to the bedrock at the other end of the bridge (the home key at the finish).

We can understand this process much better if we begin by looking at how the basic chords of any key are constructed, and how they actually relate to each other.

Major Scale Triads

Let’s take a simple major scale, and stack up the 1,3 and 5 notes on top of each other to form chords. Use only the notes that are actually in that scale.

These chords are called triads. You can build a triad on every note of any scale, making a total of seven chords, in this instance, in the key of C major.

Let’s number them as well. We’ll use the Roman numerals commonly used in music theory textbooks.

C Major triads
C Major triads

It might seem from the above illustration that all seven chords are of equal importance in the key of C major. But the reality is that three of the chords are massively more important, and another two have an important ‘secondary’ role in relation to these.

The Three 'Primary Colour' Chords

The I, IV, and V chords—or tonic, subdominant and dominant—are really the foundation of harmony in almost any western music genre. They certainly form the backbone of most songs we’ve ever heard. In fact many famous pop songs have been written that exclusively revolve around just these three chords alone!

In the key of G major, the I, IV and V chords are G, C and D in that order. If you play guitar, you probably learned these early on because you then would be able to play a vast number of songs in G major without necessarily needing to know any other chords.

What is the essential quality of each?

  • The tonic (or root key) is our home key. It’s often the starting point of our song, and almost certainly the end point as well. In the key of C major it is C. The feeling of the home key is one of stability and equilibrium.
  • The subdominant gives a sense of ‘travel’ to our next important harmonic place; an adventure begins. In the key of C major it is F. After arriving here, we can return to the home key, or decide to venture further.
  • The dominant is a vital harmonic pivot point in harmony; it conveys a strong ‘desire’ to return home and is often followed by the home key, either at the end of the piece or in order to start a new sequence of events. In the key of C major, it is G.

In a major key, each of these three ‘primary colour’ chords is actually a major chord; that is to say, the interval between the bottom note and the middle note is a major third (the higher interval is consequently a minor third). If you are unclear how intervals are named, Ryan Leach has already written a very good article on this: Music Theory: Intervals, and How to Derive Them.

The Twelve Bar Blues

This was the basis of nearly all early blues and so-called ‘boogie-woogie’, and illustrates perfectly the important of the three main chords we’ve described and the travel of direction each implies.

12 bar blues
12 bar blues

Note that moving to the subdominant creates tension, and takes us on a journey away from the home key. We then return to the home key briefly, but somehow feel there’s more of a journey yet to come.

The dominant finally arrives as a kind of climax, before it sends us back to the tonic key once again, where the tension finds full release. In some forms of blues, the dominant is again used in the last bar, to create a kind of excitement so that the whole sequence can then be repeated.

This building of tension and then subsequent release is an ideal way to tell a story, since the harmonic energy can easily mirror the lyrics as the story progresses.

Secondary Chords Add Variety and Subtlety

If I, IV, and V are the stripped down ‘bare bones’ of harmony, then secondary chords are next in importance, as they can provide support to the main chords, add interest, or provide options within our harmonic world. Nice to think there can be a little variation of colour here and there; it also means that songs can have a more varied overall chord structure!

What are they then? Essentially there are two secondary chords, the II and the VI chord; or the supertonic and submediant chord. In the key of C major that would be Dm and Am.

Note that they are both minor chords this time, as the interval between the lower and middle notes in a minor third, with a major third above as a consequence.

The supertonic chord can lift or pave the way for the dominant chord by being used just before it. By virtue of it being a minor chord, it can lift us to the more positive sounding dominant major chord; this effect is enhanced when a seventh is added to it.

Compare them both in this next illustration:

Supertonic chords
Supertonic chords

The submediant can be used as an alternative to the subdominant chord. Sometimes it also can precede it; again the minor giving way to the more forceful sounding major chord.

The chord structure of ‘Chopsticks’ shows this: the actual chord progression behind it in the key of C major is C Am, F G. This chord progression has been commonly used over and over again in all kinds of ways.

The strength of so-called secondary chords lies in the closeness of their relationship to the root or tonic key; we will discuss this in a bit more depth later on.

The Circle of Fifths

There’s no rule that says you have to remain in one key throughout the whole of your piece of music. Changing the ‘home’ key of your song is called transposing, and this is often accomplished by using a ‘pivot’ chord that ‘sends’ the music to the new home key; perhaps a bridge or ‘middle-eight’ section that has a total change of mood before the return of the final climactic chorus in the original key. The transposed key might be the next one around the so-called ‘Circle of Fifths’, either in a clockwise or anti-clockwise direction, since these keys are most closely related to each other.

In the following illustration, you might notice that travelling in a clockwise direction each key has one more sharp or one less flat in its key signature, with the key in the ‘6 o’clock’ position being either F# major or Gb major depending how you look at it. The Circle of Fifths is also sometimes known as the Cycle of Fifths.

Circle of fifths
Circle of Fifths. Image Copyright © Sienna M. Wood, 2015, via Music Crash Courses

Notice that the inner circle lists minor keys that share the same key signature as the major key adjacent to it. These are the relative minor keys. So A minor is the relative minor of C major; C# minor is the relative minor of E major, as so on.

Now it’s possible to see why the VI chord is an important secondary chord; it is because it’s the relative minor of that major key (the VI chord in C major is A minor). Similarly, the II chord is important because it can potentially become the dominant of the dominant, simply by raising the third of the chord to become a major key.

So in C major, the D minor chord can become the dominant of G major simply by changing into D major. Once that’s done, it has the effect of transposing or ‘sending’ the music to the new home key of G major, one step around the circle of fifths.

Minor Scale Triads

Before we conclude this article, it’s worth taking a look at how triads stack up in a minor key. We’ll stick to the harmonic minor scale, as the melodic minor uses different notes coming down the scale as the ones you use going up!

Here’s how it works in C minor:

C Minor triads
C Minor triads

Notice two of the ‘primary colour’ chords (I, and IV) are now minor, whereas V has remained a major chord. So whether you are in a minor or a major key, every V chord will always be major.

Looking at the secondary chords, VI is now a major (in fact the relative major; Ab is the relative major of C minor), but the II chord has shrunk to a diminished chord since both the top and bottom intervals are minor thirds. It is called ‘diminished’ because the interval between the top and bottom notes is no longer a perfect 5th, but a diminished 5th.


In the next article, we’ll take a look at chord inversions, three- and four-part harmony, pedal points, suspended and diminished chords, how to spread chord voicings in a more pleasing manner. We'll also check out a few song examples that illustrate some particularly awesome chord progressions!

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