Dominant - simple, yet sophisticated.

Dominants have been the staple of music for hundreds of years.  Every time you listen to a song, by the end you've heard the dominant do it's thing more than a couple of times, maybe you knew it, but you probably didn't know how much you did.  Dominants are there even when it doesn't seem like it. 

When I say "dominant" I am refering to, in it's most basic form. The fifth note of the scale.  This is the dominant note.  Maybe not the most important note, but arguably so.  On this note, is built the dominant chord, the V chord.  You may remember the from the cadence lesson the term perfect authentic cadence. This refered to a V to I cadence.  This cadence is the most powerful cadence in music. 

But why?

If you take a look at the following picture you will see how the V chord (in C Major) moves to the I chord. 

The G stays the same as it is the common tone.  The B moves to the C.  The D moves to the three.  Now this is important to remember.

Basic Tone Movement

When our ears hear a scale.  We have it set in our brains what to expect the tonic to be.  If you've played a major scale but stopping at seven you will notice your ear NEEDS to hear that seven go to tonic.  That's because in a scale certain tones lean towards other.  These spots include:

7th to Tonic

4th to 3rd

2nd to 3rd

Therefore the 7th WANTS to go to the tonic and, to our ears it feels right when it does.  Same for the 4th and the 2nd.  So take a look at that progression from earlier.

You will see the in the G Major chord there is a B (7th of scale) and a D (2nd of scale).  So... in any dominant chord you have a common tone, a 7th, and a 2nd.  All three tones lead to the I chord.  It is like a match made in heaven.

Dominant 7th Chord

Now a normal V chord will feel powerful enough.  But...there is also a 4th to 3rd relationship that would make it even more powerful. 

If you examine the picture below it is the same as the last, only I've added an F to the V chord making it a dominant 7th chord.  

F is the 4th scale degree in the key of C Major.  And where does the 4th want to go...to the 3rd.  In this case, E, which happens to be in the I chord as well.  Another perfect fit. 

For these reasons, the dominant chord and dominant 7th chord are the backbone of chord progression.  You'll learn more on how tone leading defines how progressions sound and work.