Dominance

So when we talked about scales we touched on the idea of tonality. To recap, tonality is the idea that melodies (and chords) naturally gravitate towards the tonic. When we talked about intervals we touched on consonance and dissonance. Just to remind you:

Early music was written largely for voice. In fact a whole chunk of theory was created to ease writing for choirs or duets. Now some intervals are easier to sing than others. To be brief and blunt we call intervals that are easy to sing consonant and intervals that are hard to sing dissonant. Music revolves around the idea of creating dissonance only to resolve it. The goal is to create some kind of tension and have it resolve only to move to some other tense harmonies. Dissonant intervals are these tense intervals because when we hear them we naturally want to resolve them into consonances.

The consonant intervals are:

All major and minor intervals except major seconds and sevenths
All perfect intervals

The dissonant intervals are:

Major and minor sevenths and seconds
All augmented and diminished intervals"

If you recall from our discussion of minor scales we talked about the subtonic (flat 7th scale degree) being a whole tone below the tonic (1st scale degree). We noted this as a problem and for that reason composers came up with the harmonic minor scale where the 7th scale degree is raised so we call it the leading tone. Just to remind you here's what it looks like in A minor:

A B C D E F G# A

Now remember from chords that we didn't call the minor triad that we formed on the fifth scale degree the dominant. Let's reexamine the minor scale as a series of triads but with the seventh scale degree raised (i.e. the harmonic minor scale).

E F G#A B C D   E
C D E F G#A B   C
A B C D E  F G# A
1 2  3  4  5  6  7   1

What's different?

We'll since the only note we changed was the G to a G# the only chords we changed were the ones that had a G in them. These chords are the mediant (3), dominant (5), and the leading chord (7).

These are the dominant chords. Let's talk about why.

As I said before, the leading tone in a scale always wants to jump up to the tonic. This happens because music has tonality, a gravity towards the tonic, but it happen the most here because the leading tone is so close to the tonic. It's even more present in the leading tone than any other note because we're more accustomed to wanting to go up to a note then down. So we can look at the leading tone as the most predictable note, it always needs to go up to the tonic. This is what makes a dominant chord a dominant chord.

Now we're going to leave the mediant out of our discussion for a little while and focus on the other two dominant chords, the dominant and the leading chord.

First the dominant. Whether in major or minor keys, the dominant is the same chord, major. The most important aspect of the dominant chord is the middle note (the third) which in terms of scale degrees is the leading tone, scale degree 7. For the most part, dominant chords always move to tonic chords. This all revolves around the idea of resolution.

A chord of particular interest is the dominant seventh chord. Looking at the major scale with stacked thirds to form seventh chords, we'll see that scale degree 5 is the only one that forms a dominant seventh chord.

B C D E F G A B
G A B C D E F G
E F G A B C D E
C D E F G A B C
1  2  3 4 5   6  7 1

We're particularly interested in this chord because of a very specific interval contained within it called the tritone.

The tritone is a diminished fifth or augmented fourth interval that is formed between scale degrees 7 and 4 (the third and seventh of the dominant seventh chord). In classical music, the tritone has a very specific resolution (a way of moving from dissonance to consonance). As we discussed, scale degree seven moves upwards to the tonic (scale degree 1) and scale degree 4 moves downwards to scale degree 3.

Our diminished seventh chord also contains a tritone between its root and fifth and should be treated with the same resolution. While our discussion has mostly revolved around the V chord just about anything we've said about dominance applies to all dominant chords.