Every afternoon I walk home from school. 
I'm getting bored of taking the same path every day.
It's getting less and less exciting. 
Hmm.
This way looks more vividly vibrant.
Maybe it’s time to take a more exciting way home. 
Wow this is so amazing! 
Look at all the colorful tiles! 
Look at these murals! 
Mind blown. 
Such a colorful neighborhood.
And even though I took the new route of secondary dominant road.
I still came home. 
This is the fundamental concept behind secondary dominants. 
In music, we try to keep the music interesting in the same way
taking different routes to get to the same destination. 
Take this common sequence of chords. 
With a small modification, 
we can make this sound less predictable, 
keeping it interesting.
In a major scale, the V chord includes the leading tone. 
This tension wants to bring you back to home to the I chord. 
We call this chord, the dominant chord. 
These primary tonic/dominant chords function to establish key. 
Similarly, a secondary dominant brings you to a temporary home key, still ending up at the original home. 
These help create the sense of a new or different tonic due to the secondary leading tone that pulls to this new tonic. 
This process is called tonicization. 
When a diatonic major or minor chord is temporarily being treated as the tonic itself. 
If you decide to stay in this new tonic longer, it’s called a modulation. 
A secondary dominant is any M or Mm7 chord that temporarily functions as the dominant. 
To achieve a secondary dominant, first, we take a chord in the scale that we want to go to. In C, let’s go to Dm which is the ii. 
Then we place the chord of the relative dominant to the chosen chord before it. 
The V refers to the secondary dominant and its relation to ii. It's the dominant of ii. 
The ii refers to the tonicizing chord's function in the original key. 
So here, we have a V of ii chord going to ii and we’ll end the progression with the original V7-I. 
To wrap up, let’s review what we learned. 
Secondary dominant chords add harmonic color because they’re unexpected. 
They’re always non-diatonic in the key, major triads or major-minor seventh chords, and tonicize a diatonic chord in the key. 
It is not a modulation because the tonal center is changed only temporarily. 
To create a secondary dominant, pick any chord in the key, except diminished, then precede it with its relative dominant chord. 
Understanding secondary dominants enhances our ability to compose, improvise, perform, and appreciate music. 
