Topics covered on this page: The tertian system – Basic triads – Major triads – Minor triads – Diminished triads – Augmented Triads – Triads generated from major and minor scales

Harmony is one of the building blocks of basic music. As opposed to melody which are tones sounding sequentially, harmony is where the tones are sounded together. Triads make up the foundation for harmony and is what will be looked at in this section.

There are four type of triads based off the major or minor scales: major, minor, augmented, and diminished. These names may sound familiar if you have already covered the intervals section where they are introduced. A triad can be formed on any note of a scale. Depending on what scale degree the triad is formed, the triad will function as the tonality within that scale.

Said another way, a triad is simply scale degrees 1, 3, and 5 played together. A C major triad built upon the 1st scale degree of a C major scale is: C-E-G:
A D minor triad built upon the 2nd scale degree of a C major scale would be the 1st, 3rd, and 5th tones starting on D. Or, D-F-A:
Remember that two tones sounded together is called an interval:
Three tones or more sounding together is called a chord:
In discussing this section we will say that triads are three different notes (with less basic chords, notes are doubled sometimes).

Triads are of particular importance for a basis of music theory because intervals of three make up the tertian system of harmony. Tertian means essentially relating to three. Triads are built off of the interval of a 3rd in tertian harmony.

As mentioned, both a triad and a scale may start on any note in a basic scale. These are basic triads. Take a look at the examples below showing the scale-triad relationship of the major scale (triad notes are highlighted in red).

C major scale:
C major triad:
D minor triad:
Here a B note has been added to the first of a C major scale to show a B diminished triad:
Note, the augmented triad is not found as a triad form the basic scale as the major, minor and diminished are.

Examine the intervals in the C major triad below…

From 1 to 3 in a C major triad is a major third:
From 3 to 5 in a C major triad is a minor third:
From 1 to 5 in a C major triad is a perfect 5th:
The whole C major triad:
The three types of basic triads found in a basic major or minor scale are: major, minor, and diminished.

A major triad will have the 1st, 3rd, and 5th scale degrees of a major scale.

In C major this will be C-E-G:
In G major, for example, this will be G-B-D:
Remember, the starting note of a triad (as is the case with scales) gives a strong base for the tonality for the rest of the triad. It is the lowest tone of the triad and is called the root. The highest note in a triad is the 5th. Lastly, the middle note in a triad is called the 3rd. By following the correct interval rules of a triad, triads can be formed on any note.

Minor triads are built in the same way as major triads. By using the 1st, 3rd, and 5th scale degrees of a minor scale a minor triad is created.

A closer look at minor triad intervals…

Intervals 1 to 3 create a minor third:
Intervals 3 to 5 create a major third:
Intervals 1 to 5 create a perfect 5th:

Note that the order of thirds in major (major 3rd to minor 3rd) is reversed in minor (minor 3rd to major 3rd). This chart below summarizes…


We see that the interval from 1 to 5 in both major and minor triads are the same. Also we see that the interval qualities are reversed in 1 to 3 and 3 to 5 in major and minor triads.

Below are where major and minor triads are found in the basic C major scale. There are three basic minor triads: D-F-A, E-G-B, and A-C-E. They are the 1st, 3rd, and 5th tones of the starting scale degree.

Minor triad D-F-A:
Minor triad E-G-B:
Minor triad A-C-E:
Note, in the last example the basic C major scale has been extended by two notes to allow the triad notation.

An augmented triad can be formed by raising the 5th in a major triad a half step. An augmented triad can also be formed by lowering the root and 3rd of a major triad by a half step. By examining the intervals contained in the augmented triad we notice the following: from 1 to 3 is a major third, from 3 to 5 is a major third, and from 1 to 5 is an augmented fifth. So two major third intervals create an augmented triad.

C augmented triad:
Interval 1 to 3 in C augmented triad (major 3rd):
Interval 3 to 5 in C augmented triad (major 3rd):
Interval 1 to 5 in C augmented triad (augmented 5th):
Diminished triad are formed from lowering the 5th of a minor triad a half step. Another way it can be formed is by raising the root and third of a minor scale a half step.

Minor triad and diminished (lowering the 5th of minor triad):
Minor triad and diminished (raised root and 3rd of minor triad):
As with the augmented triad, the diminished triad is named for the diminished 5th interval between 1 and 5. The interval between 1 and 3 is minor, the interval between 3 and 5 is minor, and the interval between 1 and 5 is a diminished 5th. Two minor thirds in succession create a diminished triad.

Interval 1 to 3, or a minor 3rd:
Interval 3 to 5, or a minor 3rd:
Interval 1 to 5, or a diminished 5th:
A diminished triad:
Remember, in the basic scale of C major, a diminished triad only found in one place: starting on the 7th scale degree with notes B-F-D:
Examine the basic triad on each note of a G major scale below. As with all major scales, the triad order is:



Major triads on scale degree 1, 4, 5

Minor triads on scale degree 2, 3, 6

Diminished triad on scale degree 7

Alternatively, we can use roman numerals (uppercase for major, lowercase for minor) to describe the scale degrees as well:

Since we covered the harmonic minor scale in an earlier section, we will now examine the triads that it produces. Up to now we have only been looking at basic triads from basic major and minor scales.

The harmonic minor scale:
There are two major triads, two minor triads, one augmented triad, and two diminished triads in the harmonic minor scale.

Major triads on scale degree 5 and 6
Minor triads on scale degree 1 and 4
Augmented triad on 3
Diminished triads on scale degree 2 and 7

Another way to describe qualities of the triads or chords is to use roman numerals or uppercase/lowercase. Uppercase means major and lowercase means minor:


The chart below summarizes the triads covered in this section:



To review what was covered earlier, the major scale with its triads and Roman numeral equivalent is shown below:


The harmonic minor scale with triads:

This is the end of the theory primer… go back to music theory index¬†or sight singing exercise index ?