Harmonizing the Major Scale I: Triads

The process of harmonizing a scale involves building chords on each degree (note) of the scale, using only notes from that scale.

This post will:

Take us through the process of harmonizing the major scale with triads.
Analyze the chords that result, along with the Roman numerals assigned to each chord.
Show the relationship between the chords in a harmonized major scale and the scale itself.
Provide instruction on how that relationship relates to soloing on a guitar.

Building Chords

Most chords are built in intervals of thirds, meaning the distance between one note in a chord and the next highest note is three scale steps (a more detailed analysis of intervals will be provided later in the series).

For example, a C major chord contains the notes C, E and G — the first, third and fifth degrees of a C major scale (fig.1).

Fig.1

The distance between the C and the E is three scale steps (C, D and E).

And the distance between the E and the G is three scale steps (E, F and G).

Harmonizing a Major Scale

To harmonize a major scale with triads, we need to take each note in the scale and add two notes above it, each one three scale steps higher.

Harmonizing a C Major Scale

Harmonizing the First Scale Degree

The C in a C major scale is harmonized as described above, by adding an E and a G (fig.2).

Fig.2

Harmonizing the Second Scale Degree

The D in the scale is harmonized by adding an F and an A (fig.3):

The distance between the D and the F is three scale steps (D, E and F).
The distance between the F and the A is three scale steps (F, G and A).

Fig.3

Harmonizing the Third Scale Degree

The E in the scale is harmonized by adding a G and a B (fig.4):

The distance between the E and the G is three scale steps (E, F and G).
The distance between the G and the B is three scale steps (G, A and B).

Fig.4

Harmonizing the Fourth Scale Degree

The F in the scale is harmonized by adding an A and a C (fig.5):

The distance between the F and the A is three scale steps (F, G and A).
The distance between the A and the C is three scale steps (A, B and C).

Fig.5

Harmonizing the Remaining Notes in the Scale

The remaining three notes in the scale (G, A and B) are harmonized using the same method. A fully harmonized C major scale is shown in fig.6.

Fig.6

Chord Analysis

Now that we have harmonized a C major scale (we have built chords on each degree of the scale), we can determine the quality of each chord using the chord formulas detailed in the post entitled Triads and Chord Formulas.

An analysis of each chord is provided below:

The first chord contains the notes C, E and G — the first, third and fifth degrees of a C major scale, so the first chord is C major (fig.7a).
The second chord contains the notes D, F and A — the first, flatted third and fifth degrees of a D major scale, so the second chord is Dm (fig.7b).
The third chord contains the notes E, G and B — the first, flatted third and fifth degrees of an E major scale, so the third chord is Em (fig.7c).
The fourth chord contains the notes F, A and C — the first, third and fifth degrees of an F major scale, so the fourth chord is F major (fig.7d).
The fifth chord contains the notes G, B and D — the first, third and fifth degrees of a G major scale, so the fifth chord is G major (fig.7e).
The sixth chord contains the notes A, C and E — the first, flatted third and fifth degrees of an A major scale, so the sixth chord is Am (fig.7f).
The seventh chord contains the notes B, D and F — the first, flatted third and flatted fifth degrees of a B major scale, so the seventh chord is B° (fig.7g).

A harmonized C major scale with the chords labeled is shown in fig.7.

Fig.7

Diatonic Chords

The term diatonic refers to notes and chords found within a scale or key.

The chords that result from harmonizing a scale are considered diatonic (or natural) to that scale and key.

The chords we built above — using only notes from a C major scale — are diatonic to the key of C major. In other words, the notes contained in the chords are all found within a C major scale.

For example:

An Am chord is diatonic to the key of C major because the notes A, C and E are all found within a C major scale.
An F (or F major) chord is diatonic to the key of C major because the notes F, A and C are all found within a C major scale.

Roman Numerals

Every major scale has seven triads that are diatonic to it, one chord for each scale degree.

Each of the seven diatonic chords is assigned a Roman numeral, which reflects the chord’s position within the key, relative to the tonal center (the first note or chord).

Uppercase numerals are used for major chords and lowercase numerals for minor chords. A diminished chord is represented by a lowercase Roman numeral with a small circle after it.

The Roman numerals representing the chords diatonic to the key of C major are shown in fig.8.

Fig.8

Sequence of Chords

Every harmonized major scale has the same sequence of major, minor and diminished chords. As the sequence of chords is the same in every key, the sequence of Roman numerals is also identical.

In any given major scale or key, the diatonic chord qualities are as follows:

The I, IV and V chords are major.
The ii, iii and vi chords are minor.
The vii° chord is diminished.

All 12 Harmonized Major Scales

All 12 harmonized major scales are shown in fig.9.

Fig.9

Soloing Application

What this means with regard to guitar playing is that you can use a major scale to solo over any of the chords that are diatonic to it because the notes generally won’t clash with the chords.

And if all of the chords in a progression are diatonic to the same major scale, you can use that scale to solo over the entire progression.

For example, if all of the chords in a progression are diatonic to a C major scale, you can use a C major scale to solo over the progression.

The chord progression in fig.10 contains four chords all diatonic to a C major scale (C, Am, Dm and G). So you can use a C major scale to solo over the progression.

In the key of C major:

C is the I chord.
Am is the vi chord.
Dm is the ii chord.
G is the V chord.

Fig.10