Tonic and Dominant Relationships

Before delving into other chords or any other information, the first thing to do is to strengthen your understanding of chord progressions. You need to study the relationship between tonic and dominant chords, especially the dominant seventh and the diminished chord that often substitutes for it.

In the last chapter you saw how strong a pull the leading tone could have by playing a scale and stopping on the leading tone, leaving the scale yearning to resolve. You also played a single dominant seventh chord and let it hang out to dry, so to speak. Both the leading tone and the dominant seventh chord felt unresolved. In the case of the leading tone, you achieved resolution by completing the scale, playing the full scale, and concluding on the tonic note. Resolving the chord required playing another chord after it. The fact that the dominant seventh chord was acting as a V7 chord was solidified by its resolution to a I, or tonic, chord.

Harmonically speaking, the existence of a V7 and I (or i) chord indicates that you are in the key of the tonic chord. That's all you need when it comes to harmony to define what a key is.

It has always been a challenge to define a key clearly. In tonal music, and especially in the common practice period that music theory so often studied, the tonic dominant relationship will identify exactly what key you are in. Now, look at what makes a dominant chord pull so strongly to the tonic chord.

Voices in Motion

The relationship between V and I is all about tension and release—yin and yang and balance. V chords, especially when they have sevenths and even more when they are substituted by vii (diminished) chords, are extremely tense. The tension lies in the chord itself. Look at the V7 chord in FIGURE 10.1 and see what you have.

FIGURE 10.1 Dominant Seventh Chord Exposed!

Stay in the key of C major to keep it simple. The G7 chord shown in FIGURE 10.1 contains the following tones: G, B, D, and F. Now, remember what you learned about leading tones. Remember how strong they are? In the key of C, the leading tone is the seventh degree of the scale, which happens to be a B. The G7 chord has that note in it. Within the C scale is another leading tone of sorts. Between the fourth and third degree is another half step. When you stop on the fourth degree of the scale (F), it pulls down to E fairly heavily. It's nowhere near as dramatic as the pull from B to C, but it is there. Check it out in FIGURE 10.2.


FIGURE 10.2 The Pull from 4 to 3

In that example, you heard a full scale, which went up to the fourth above the octave (which still counts as the fourth). Again, the note does not want to stay there; it has gravity of its own and pulls back to the third of the scale. In a V7 chord, you have the other leading tone (F). So, in one chord, two unstable tones are played together at the same time—no wonder it sounds tense! But wait, there's more. You can go another step deeper into this chord. Since B and F have been identified as tension notes within the dominant chord, look at the interval that they produce (see figure 10.3).


FIGURE 10.3 B and F

By taking these notes out of the chord and playing them together, you can get an even better sense of what's going on. The interval from B to F is a tritone, the most unstable and dissonant interval you would deal with on most normal days. Not only does the V7 chord contain both leading tones (the fourth and seventh of the scale), but the interval created between those tones is a tritone (another unstable sound). This chord is clearly waiting to do something.

The B and the F need to resolve. The B wants to go up to C. The F wants to move down to E. You already have a G, in the G7 chord, so it doesn't need to move. Right there, you spelled the resolution of V7 to I (see figure 10.4). The D in the G7 chord can resolve to either C or E in the C chord. Either way you slice it, the third of the G7 chord must go up and the seventh of the G7 chord must go down.


FIGURE 10.4 A Good Resolution

That's it, folks. If you can grab on to this, you will understand tonality. The relationship between V and I is the cornerstone of tonal harmony. Sure, there is music that doesn't make heavy use of it, but you'll see more dominant to tonic chords than you will know what to do with once you learn to see them.

The diminished chord in the major scale (vii°) often substitutes for V. It has a dominant function because it also pulls very strongly to I. The vii° chord contains both the leading tones discussed earlier and, if spelled as a fully diminished seventh, it adds an additional leading tone (the lowered sixth of the scale), which pulls down to a note in the tonic chord. This is why V and vii° can substitute for each other. Now it's time to talk about minor keys and their chord progressions.

One of the reasons that the relationship between dominant and tonic chords is so important is that if you inventory the tones between both chords, you essentially spell the entire scale out (well, almost entirely). The C and G7 chords combine to give C–D–E–F–G–B–C (a C major scale, excluding A). That's exactly why two chords can tell you what key you're in; they spell it out for you with their tones.

Minor Chord Progressions

Minor scales come directly from major scales. So when you create diatonic triads, you'll have the same triads you had with the major scale; the only difference is that the Roman numerals will change position.

Look at a diatonic B minor scale, harmonized into triads, in FIGURE 10.5.

FIGURE 10.5 Diatonic B Minor Triads

Compare this with the related major key of D major in FIGURE 10.6. You will see the same triads, just in a different order.

FIGURE 10.6 Diatonic D Major Triads

When it comes to the chord ladder, the minor key doesn't look all that different from the major version of the chord ladder. FIGURE 10.7 presents the minor chord ladder.

FIGURE 10.7 Minor Chord Ladder

You will notice a few things:

  • The ladder progresses in movements of fifths, just like the major chord ladder.

  • The substitute chords always share two notes in common with their possible substitutions.

  • The V and vii° chords look funny. Compare them to the diatonic triads in FIGURE 10.5 to see two main differences:

  • The V chord has been changed from a minor triad to a major triad.

  • The vii° chord has not only changed from a major triad to a diminished triad, but its root has also moved up one half step.

What would cause such dramatic changes in the minor scale? To put it simply, it's not the same scale (the natural minor scale). Harmonizing in minor keys, 99.9 percent of the time, uses the harmonic minor scale to give a major (and dominant seventh) chord on V and a fully diminished chord on vii° (which creates a diminished chord on the leading tone and substitutes for V7).

The importance of the relationship between V and I was discussed at the beginning of this chapter. The relationship is just as important in the minor scale. The natural minor scale does not have the proper V chord (diatonically, it's minor), and the VII chord does not substitute or pull up to the tonic either. So add a raised leading tone to the scale (raised seventh tone), which affects the V and vii° chords, making them both true dominant chords. Look at the effect of these new chords on some sample chord progressions in minor keys.

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