Primary Triads and Their Functions ① / Music Theory Lesson

Author: sleepfreaks

Understanding Chord Functions to Create Developing Progressions

This time, we will be looking at information that will give us insight on how to create a song
with a sense of “story” and “development” using the major diatonic chords we have touched upon.

First, give a listen to the audio below:

In this audio we simply lined up major diatonic chords from a specific key without much thought,
and the progression doesn’t feel like it flows.

In fact, each diatonic chord has a specific Function,
and simply lining up chords at random will make it difficult to create a song with
a proper sense of story (beginning, development, twist, end).

Primary Triads

As the first step, lets take a look at the 3 most important chords – the primary chords.

First refresh your memory on what we learned about each scale degree in the previous article.
This time we will be using the easy key of C as an example.


Here we took a look at some terms,

  • Tonic
  • Subdominant
  • Dominant

including the 3 mentioned above.
These 3 words hold incredible importance in a chord progression.
With this in mind, lets move forward.

Next, lets layer notes of the C major scale to create the C major diatonic chords.
If you’re not sure how to do this check out our previous articles:

Major Diatonic Triads
Major Diatonic 4 Note Chords (7th)

  • Triads


  • 7th


Here, take a look at the Tonic, Subdominant, and Dominant chords.
These are called the Primary chords.

In addition, these three have their own specific fuction, and are often displayed with the letters below:

  • Tonic = T
  • Subdominant = SD (sometimes written as S)
  • Dominant = D

Although there are other chords with similar functions to the above,
the importance of the primary triads is undeniable.

We will be looking at this concept in further detail in our next article, but for now keep in mind that
the primary triads are the chords that have the I, IV, and V notes from the scale as the root note.

Chord’s Function Changing Depending on Key

Last, we will be taking a look at an key point where many beginners may make a mistake.

A chord by itself does not have a particular function; in fact, the function is in relation to it’s placement in the key (scale degree number).

Using the same image from our last article, lets take a look at C.

In the C major scale, it is the first on the left.


If we make a diatonic chord from it,



of course, it will be the “I” chord. Though it is the tonic chord made from the tonic of the scale,
in the G major scale the C is the 4th note.


If we make a diatonic chord from it,



it will be the subdominant “IV” chord.

As seen, despite being the same chord, it holds a totally different function depending on the key it is in.

Though we have continued a number of articles looking at theoretical knowledge,
in our next article we will be using sounds to begin finding the meaning behind these functions.

Article Writer: Kazuma Itoh

講師 伊藤
After moving to the USA at 18 years of age with a scholarship from Berklee, he completed a 4 year study focused on song writing and arranging there.
Using this knowledge, he works across a variety of fields from pop music, film music, and more.