As a lifelong professional guitar player, part of what I do is teach. This article (reposted from my website, StringDancer.com) is specifically for guitarists seeking understanding of basic music theory as it applies to guitar. It won't be of much use to non-musicians, but I'm just curious what kind of response it might get here on Steemit. Thanks.
A key is a range of notes used to construct melodies and chords. Any song can be performed in any key, as the relative construction of the tune stays the same. Changing the key merely raises or lowers the range. The most common use of keys is to position the range of notes sung in a tune to fit comfortably with a particular singer. You may have experienced this yourself sometime when you tried to sing a song in one key, but the melody felt too high or too low for your voice. By changing the key, virtually any song can be optimized for your particular voice. Using barre chords, you can play a tune in any of the 12 major keys (and their 12 relative minor keys) on the guitar.
But there are five primary keys which we say "lay well" on the guitar. These are keys that have a lot of simple open chords, minimizing the need for more difficult barre chords. Many highly successful songwriters, in fact, only know the chords indigenous to these five primary keys, and it certainly doesn't limit them in their ability to write great songs. By the way—by utilizing a capo with these simple chords, one can play in any key by simply positioning the capo at the appropriate fret to change the key center of the chords.
The five primary keys are often referenced by the term "the CAGED system", the keys being C, A, G, E and D. Here is a chart of the five primary keys and the seven chords they each contain. The seven chords take their roots from the notes in the major scale for the chosen key (do-re-me-fa-so-la-te). You will notice that many chords are used in different keys, so the actual number of chords to learn is fewer than you might think.
CAGED Keys
Column Colors and What They Mean
The blue columns (light blue corresponding to the I and IV chords, and darker blue to the V chord) are all built on a major triad (1 3 5), and are often called the Three Principle Chords (no matter what key). The I and IV are considered pure major chords, as if extended beyond a triad they will contain a major 7th (1 3 5 7). The V chord as a triad is major, but if extended contains a flatted 7th (1 3 5 b7), and is thus differentiated by the term "dominant chord". In practice, the V chord can be played as either major or dominant interchangably. Your ear will tell you which version sounds best in context. The green columns (light green corresponding to the II, III and VI chords) are all built on a minor triad (1 b3 5). If extended, all three will contain a flatted 7th (1 b3 5 b7).
Types of Chords
While each key has seven chords which occur naturally in that key, upon further study we discover that the seven chords consist of four chord types. Think of them as chord flavors, if you like. We have:
Major, with a construction of 1, 3, 5 (if extended, it will have a 7)
Minor, with a construction of 1, b3, 5 (if extended, it will have a b7)
Dominant, with a construction of 1, 3, 5 (if extended, it will have a b7)
Diminished, with a construction of 1, b3, b5 (if extended, it will have a b7)
The natural chords in any key occur in this order:
I - major
II - minor
II - minor
IV - major
V - dominant
VI - minor
VII - diminished
So the I and the IV are major. The II, III, and IV are minor (to help memorization with the minors, think "2 times 3 equals 6").
The V is a sort of hybrid, it can be played as either a straight major or as a dominant (commonly called a "7th") chord.
And lastly, the VII is a min7b5 chord. Note that "VII chord" and "7th chord" do NOT mean the same thing!
The VII Chord - Diminished
The darker green column in the chart highlights the VII chord, the only chord indigenous to the major scale that contains a diminished fifth (1 b3 b5), making what we call a diminished triad. It's commonly called a "minor 7 flat 5 chord" because if extended, it also has a b7. NOTE: Veteran jazz players often refer to the VII chord as a "half-diminished" chord, similar to (but differentiated from) what's called a diminished 7th chord, which is constructed a little differently: 1 b3 b5 bb7 (A 'double-flat 7' can also be thought of as a major 6). The m7b5 chord appears less often in tunes written in a major key, but is quite common in minor-key tunes. A common minor key progression might be something like:
➤ ||: Bm7b5 E7 | Am :||
So What Does All This Do For Me?
It's fair to say that if you can play the indigenous chords found in the Five Primary Keys, you would be able to play 90% of the songs you want to play without further chord study. Tens of thousands of songs in many genres of music only use the three principle chords (I, IV and V). Thousands of other tunes might use the three principle chords and just one or two others, most notably the II chord and the VI chord. Rarely will a song utilize all seven chords in a key, though it can happen. And while there are many tunes which make use of what we call outside chords (referring to any chord which does not occur naturally within a specific key), it's very likely you would know that chord anyway if you know all the chords listed in the chart. And of course, by using barre chords, any chord becomes readily available on the guitar in a variety of positions.
Copyright 2009 Jeff Foster. All Rights Reserved.
