I am close to completing Guitar Fundamentals 2 and may have missed something in an earlier lesson. The video "BARRE CHORDS LOVE THE 'MAGIC L'!", Lisa is talking about the first six chords in the key of G. These are: G, Am, Bm, C, D, Em. What is the music theory behind this progression? I'm a logical kind of guy and like to understand - not just memorize.
Chords in any Key
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Let's break down a major key...
In the key of G major the notes are
G, A, B, C, D, E, F#, (G)
Then we built a triad chords from these notes taking a root, a third and a fifth note.
G - B - D
A - C - E
B - D - F#
C - E - G
D - F# - A
E - G - B
F# - A - C
Now let's analyze the intervals of each triad
G - B - D
is a root, a major third (four half-steps) and a perfect fifth (seven half-steps from a root). There is a major third interval, this makes a chord major, G major in this case.
A - C - E
is a root, a minor third (three half-steps) and a perfect fifth. There is a minor third interval, which makes a chord minor, Am in this case.
B - D - F#
is a root, a minor third and perfect fifth. Again a minor third interval. The chord is a minor, Bm.
C - E - G
is a root, a major third and perfect fifth. This time a major third interval. The chord is a major, C.
D - F# - A
is a root, a major third and perfect fifth. Again a major third interval. The chord is a major, D.
E - G - B
is a root, a minor third and perfect fifth. Again a minor third interval. The chord is a minor, Em.
F# - A - C
is a root, a minor third and diminished fifth (six half-steps from root). The chord is a diminished, F#°.
In general
- all the triad chords with a root - [u]a major third[/u] - perfect fifth are major chords.
- all the triad chords with a root - [u]a minor third[/u] - perfect fifth are minor chords.
The major key triad chord formula is always
major - minor - minor - major - major - minor - dim
regardless of what key we are in.
In G major this is G - Am - Bm - C - D - Em - F#°.
The chord degrees are typically marked using a roman numerals, so, that major chords are marked with a UPPERCASE letters and minor chords with a lowercase.
Then the general major key chord formula is
I - ii - iii - IV - V - vi - vii°.
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