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Chord Function and Authentic Cadence is part 1 of a 10 part series on How to Write a Song.
Before we dive into chord progressions, it's important to understand why certain progressions work over and over again. Certain progressions stand the test of time, no matter the style of music.
We'll take a look at various cadences and how chords in a key have a specific function. To review diatonic chords visit: C Major Chord or C Guitar Chord. Make sure you understand the 7 chords in a major key first and this will all make sense.
All great songs have 3 things in common. They all have at least one tonic chord, a subdominant chord and a dominant chord. What does this mean?
C Maj is the I chord (tonic)
D min is the ii chord (subdominant)
E min is the iii chord (tonic)
F Maj is the IV chord (subdominant)
G Maj is the V chord (dominant)
A min is the vi chord (tonic)
B dim is the VII chord (dominant)
Tonic chords are the I chord, iii chord and vi chord
Subdominant chords are the ii chord and IV chord
Dominant chords are the V chord and VII chord
Why is this?
It's because the dominant chords have a tritone interval in them (in this case B and F) that want to resolve to a tonic chord. The subdominant chords have an F in them which creates a suspension which also wants to resolve to a tonic chord.
That's why people say you only need 3 chords to have an amazing song! It's true! In western culture, our ears have been so trained that as long as a song touches all 3 of these areas, a piece of music sounds complete.
*There are some children's, folk and country songs that only have the I and the V. They do sound complete, but they are harmonically very simplistic.
We will look at popular chord progessions in parts 2 & 3. However, at the very least you can see why the blues have endured forever.
The I chord is the tonic. The IV chord is the subdominant. The V chord is the dominant.
Now that we understand chord function, we now need to look at where these chords want to land. There are 3 important cadences to know. Typically we always want to resolve back to the I chord (or the root chord). This makes a phrase or section of a song sound complete.
An authentic cadence is simply a dominant chord (generally the V) resolving to the I chord. In this example we see a G chord resolving to a C chord in the key of C.
*a perfect authentic cadence is V to I
*an imperfect authentic cadence is VII to I
A plagal cadence is the IV chord resolving to the I chord. It's sometimes called the "Amen cadence". Here we see an F chord resolving to a C chord in the key of C.
Lastly, a deceptive cadence is just that. You go from the V chord to the vi chord, which is not the I but it is a tonic chord. Below we see the G go to Amin in the key of C.
Ok, now let's look at some excellent chord progressions and see how this all fits together!