To simplify the process of playing any song in any key, the pros use a number system. This system refers to the ROMAN NUMERALS which represent the functions of the various chords used. You might want to review the chapters on chord construction, and the use of the major scale in improvisation before going any further.
To quickly recap that info:
1. Chords in any given key center are based on scale tones.
2. By numbering scale tones we create chords built with thirds.
3. For each scale tone there is an appropriate chord, according to the key.
4. Chords have different functions which create a sense of tension and release.
5. Those functions are consistent among all keys, so the same relationships exist between chords and melodys when the key is changed.
Here is the scenario. A vocalist is sitting in with your group. She wants to sing a song you know, but has asked for it in an unfamiliar key. Let’s say for example that you would normally play this song in the key of Cmajor. The singer wants it in F major. The novice player will pray for an opportunity to write it all out, but these situations come up pretty fast and there isn’t always time to do a transcription. The pros have a trick that makes it easier.
First, look at the key of C major. The 7 chords for this key, which correspond to the major scale tones are:
I - Cmaj7
II - Dm7
III - Em7
IV - Fmaj7
V - G7
VI - Am7
VII - Bm7(b5)
Now look at the chord progression for Example #1:
Here is the same progression with a numbers approach:
The Roman numerals indicate the functions of the chords.
Now look at the new key F major.
I - Fmaj7
II - Gm7
III - Am7
IV - Bbmaj7
V - C7
VI - Dm7
VII - Em7(b5)
Here’s the same progression (I-VI-II-V) in the new key.
Apply the same concept to every key. By learning the functions of the chords, and developing a different point of view about learning a song, you can quickly change keys on the fly with many pieces of music.
Some things to keep in mind:
1. When you learn a song, plan on playing it in several keys, and apply the numbers approach to your perception of the song itself. Don’t see the song as individual chords, but rather see how each chord functions. Think of it like a language. When you learn a language, you begin with a few simple words. Eventually your vocabulary increases and you begin to talk in sentences, which grow to paragraphs, pages, and volumes. Music is exactly like that. You start with notes, then grow to chords. Now you are at that stage where you are begining to form “sentences” or chord progressions. As your “vocabulary” of phrases increases, so does your ability to “speak” clearly in the language of music.
2. The process I’ve outlined here becomes more complex when key changes occur within the actual chord progression, that are not indicated in the key signature. Start with songs that stay in one key. After awhile, you will begin to see more complex progressions. For example, you may recognize one variation as a II -V - I pattern in a different key. This will help you to remember the sections of songs which do not remain in one key.
Sometimes when we are on stage and someone doesn't know the song, we use this system to call the chord changes on the fly. The cat who doesn't know the song can follow along without too much difficulty. I was recently on a gig and the singer (Elizabeth Messina) wanted to do a tune and no one in the rhythm section knew it. As she sang the song, she showed us the numbers behind her back. We followed her through the tune with ease, and she never missed a lyric. Instant arranging, and a tribute to Elizabeth's musicality. It is rare to find singers this hip, but when you do there is no end to the fun you can have.
Special thanks to Dean Fransen for his input on this article.