Although songwriters like Hank Williams, Bob Dylan, and Harlan Howard have written many great three-chord songs, you should give yourself a few more options as a songwriter. Without getting too much into theory, I’d like to try to expand your chord knowledge in a practical and applicable way. What we want to achieve here is a stronger understanding of chords and chord progressions as used in popular music—well, all styles except classical and jazz, which are generally more harmonically complex.

When talking about chord progressions, I like to use the Nashville number system instead of words like tonic, dominant, and subdominant. The system has nothing to do with country music per se; it’s useful in understanding any chord progression in any style of music.

THE ESSENTIAL CHORDS

The chart below shows the basic chords in five guitar-friendly keys: G, C, D, A, and E.

The basic and most common chords in every key are 1, 2m, 3m, 4, 5⁽⁷⁾, and 6m. These chords are totally made up of the tones of the major scale of the 1 chord. For example, all the notes of all the chords in the key of G are made up entirely of the notes of the G-major scale (G A B C D E F# G). The C chord is called the 4 chord in the key of G because it is based on the fourth note of the G-major scale. The D chord is based on the fifth note of the G-major scale.

Let’s look at the three most important chords in any key, the 1, 4, and 5 chords. The 1 chord, the tonic, is usually the last chord of the song. A chord progression tends to resolve back to the 1 chord. The 5 chord most often leads back to the 1 chord, especially if it is a seventh chord.

Pick up your guitar and play a D chord. Notice how it sounds static or final. It could be the last chord in a song. Now play a D7. Can you hear the leading sound that implies another chord is coming? The D7 is setting up the G chord. It’s just like when you’re singing "Jingle Bells" and someone hits a seventh chord (the 5⁷) at the end of the verse while everyone sings "ohhhhh," then resolves to the 1 on "jingle bells."

So the two most necessary chords in a chord progression are the 1 and the 5⁷. The 1 is the home chord you want to get back to, and the 5⁷ chord leads you back there. If you hear a song with only two chords, you can bet they’re going to be the 1 and the 5⁷, as in "Jambalaya," "Tulsa Time," and "Achy Breaky Heart."

The next most common chord is the 4 chord. When you hear a three-chord song, it’s almost always the 1, 4, and 5 chords. The 4 chord does not imply any motion, so it’s a place to go after the 1 chord and before any other chord. You can also put a 5 chord without a seventh just about anywhere in the chord progression.

There are three minor chords common to every key: the 2m, 3m, and 6m. The 2m and 6m are the most common. The 2m often precedes the 5⁷ chord, and it can also be substituted for the 4 chord because it is the relative minor of the 4 chord. The 6m is the relative minor of the 1 chord. It can be substituted for the 1, but usually not in the last measure of a verse or chorus. The 3m, the relative minor of the 5 chord, is not as common as the 2m or 6m, but it has a sound of its own. Good examples of what the 3m sounds like can be heard in "Early Morning Rain" by Gordon Lightfoot, "Smoky Mountain Rain" by Ronnie Milsap, and "Lay, Lady, Lay" by Bob Dylan.

If you count the 5 and 5⁷ as two chords, that makes seven chords in five keys that are absolutely essential. That doesn’t mean that you have to learn 35 chords, however, because some are duplicated. It actually comes out to 19 chords. With these 19 chords, you can rule the world!