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Author:  David Luebbert Posted:  10/27/07; 3:21:59 PM Msg#:  5357 (top msg in thread) Prev/Next:  5356/5358 Reads:  3296

This is a cool question, but the explanation is kind of long.

The key identification unfortunately does not give you the name of a scale that works with all chords in a song.

In harmony, there's an idea of a home chord, a home harmony. It's a home chord because a harmonic sequence will start by sounding that chord, visit many other chords in succession and then return home at the end.

The home chord is many times, but not always, one of the first important harmonies that sounds in a piece of music. That home chord is extremely likely to be a major triad, a major 7th chord, a 6 chord, a major 9th, or 6/9 chord (you could call this the major chord family) if you are doing major harmony. If you are doing minor harmony that home chord is going to be a minor triad, a minor 7th, a minor 6th, or a minor 9th (the minor chord family).

There's also an idea in harmony of chords that are neighbors of each other. If you were working in the key of C Major, the two closest neighbors of a C major triad would be the G major triad and the F major triad. In the G Major triad, each pitch is a perfect 5th above the pitches of the C Major triad. In the F Major triad, each pitch is a perfect 5th below each pitch in C major.

Any chord is also going to have neighbors that are formed by adding a pitch that is major or minor 3rd above the top intervals in a chord which is usually the chord 5th, 7th or 9th, or by adding a pitch that is major or minor 3rd below the root of the chord. As you add related pitches to the top or bottom of an existing chords, you can also remove a pitch from the opposite side of the chord stack to create a chord relative.

There is a third class of neighbor chords which consists of any chord that can be generated by moving one or more pitches in your original chord by a major or minor 2nd up or down.

Applying this idea means that a CMA7 and a Cmi7 are close neighbors because a Cmi7 can be generated by sliding the third and seventh of the MA7 each down a half step. It means that a C7 is a close neighbor of a Dbdim7 since you get that by sliding the root of C7 up a half step.

The oldest game in making a new chord progression is to start with your home chord and travel from neighbor chord to neighbor chord in a trip that eventually leads you back to the home chord.

The identification of a key for the piece is marking the location of your home chord so that you recognize it when you return to it. The chord progression for a piece of music might return to the home chord several times during its course and then move away again.

The important rule though is that a piece won't end while its progression has moved away from home. It only ends when home is finally reached again. Usually this last occurence of the home chord will be the longest duration of that chord encountered up to that time, to signal to your ears that you've gotten back home.

You'll also usually hear that the melody is at it's most consonant when this point is reached, which gives your ears a feeling of relaxation and contentment.

In folk music, and early classical works it ended up that the neighbor chords that would be visited would only be those that fit within a particular scale. As composers got more familiar with harmony they discovered that they could make connections between chords that lead the ear very strongly in a particular direction back home. Just staying in the C major scale, they found that the progression Bmi7(b5)-Emi7-Ami7-Dmi7-G7-CMA (or CMA7) was very strong (gives a vivid sense of returning home with assurance).

The most important discovery was that you could make long chains of 7th chords that started outside of the key that could lead your ear finally to the home chord. This chain of 7th chords with that strong directional feeling is the cycle of 5ths descending (B7-E7-A7-D7-G7-C7-F7-Bb7-Eb7-Eb7-Ab7-Db7-Gb7). It's a descending cycle because the B root of chord descends a perfect 5th to E which descends a perfect 5th to A, which descends a perfect 5th to D, which descends a perfect 5th to G, etc.

Composers discovered that they could move 6 or 7 steps back in this cycle of 5ths from the home chord, start home, and that people's ears could follow this game.

And in the course of this exploration of linked 7th chords, composers discovered they could precede each 7th chord with a chain that leads to it from neighbor to neighbor. As long as the transitions from 7th chord to 7th chord happen soon enough, listeners ears could make sense of what was going on and could still recognize when a progression was heading home and when it had gotten home.

After composers became really familiar with this idea, they did not always bother with visiting the home chord at the beginning of a tune's harmony. They started to feel that some paths home were used so often in compositions that listeners would be able to tell when home had been reached even if had not been previously visited in the piece.

They also depended on the fact that after heading home the first time enroute, other later excursions home would confirm home's location because the chains of harmony always ended up there.

If you start a 7th chain back far enough, you're going to be using chords that are out of the home key. But as you progress back home you'll shed pitches that are out of the key and replace them with those that are in the home key.

When you finally get back home, you'll be playing only the pitches that make sense in the scale that contains the home chord.

Let me know if this makes sense to you.

• Re: Key of a song explained, Charles Schoonmaker, 10/31/07; 2:04:15 PM
  • Re: Key of a song explained, David Luebbert, 10/31/07; 5:35:22 PM

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