Understanding Chord Progressions

What is a Chord Progression?

A chord progression is a series of chords played in a specific order. A progression may consist of as few as two chords, but most progressions have at least three chords.

Describing Chord Progressions

There are several ways to describe chord progressions, including Roman numerals and using actual chord names. Each of these approaches are covered below.

Roman Numerals

Chord progressions are usually labeled with a series of Roman numerals where each numeral corresponds to a chord in the progression. For example, I IV vi V.

The chart below shows the Roman numeral used for the triad built on each degree of the major scale along with the type of chord. This can be used as a starting point for labeling basic chord progressions.

Scale Degree	Chord Type	Roman Numeral
1	major	I
2	minor	ii
3	minor	iii
4	major	IV
5	major	V
6	minor	vi
7	diminished	vii°

The I IV V Progression

One common chord progression is I IV V. I IV V indicates that the chord progression includes chords built on the tonic, subdominant, and dominant degrees of the major scale. The order of the chords is also important. I IV V specifies that the tonic chord comes first, followed by the subdominant, and finally the dominant.

Below is an example of a I IV V progression in C major with each chord labeled:

A chord progression labeled with Roman numerals

Benefits of Using Roman Numerals

Roman numerals make it easier to move a chord progression to different keys because they specify the function of a chord rather than a specific chord, such as C major. For example, the Roman numeral I indicates a chord built on the tonic degree of a major scale. To move this chord to another major key, you only need to find the tonic degree of the major scale for the new key. This approach can be used to transpose any chord on any scale degree to a new key.

You also need to know the type of chord built on each scale degree to use this approach. It isn't enough to know that the I chord is built on the tonic of the major scale. You also need to know that this chord is major. You can get this information from the Roman numerals by looking at the capitalization of the numerals, but it is far better to memorize the type of chord built on each scale degree.

Chords in a progression are sometimes called by the names of the scale degrees on which they are built. It is rare for an entire chord progression to be referenced this way, but you will often hear people referring to the I chord as tonic or the V chord as the dominant chord. For this reason, you should know the names of the scale degrees.

Using Chord Names

Another way of writing chord progressions is to simply write out the chord names. For example, if you have a I IV V progression in D major, you could write D G A instead. This makes it harder to transpose the progression into other keys, but may be a better method if you are working with musicians who don't understand music theory.

Nashville Number System

The Nashville Number System is a way of indicating chords with digits. This is similar to how Roman numerals work, except that you would write "1" instead of "I" for a chord on the tonic. Chord types may also be indicated by using certain symbols in addition to the digit, such as "m" for a minor chord.