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How the chords function in the key

For this lesson we are looking at the chords build from the notes of a C major scale. These are the chords that are in the key of C major. Each chord in a key has certain function within that key. The word function just means that particular chords will have a unique sound in relationship to the main chord of the key. The main chord in this case is C (C major).

To show how each chord functions in the key, Roman numerals are used as a way of labeling the chords. A Roman numeral like I, IV, or V indicates a major chord. If you see a Roman numeral with a small m after it, this is the same as seeing a letter with a small m. It means that the chord is minor. So IIm, IIIm, and VIm are all minor chords. The small circle after a Roman numeral means diminished, like VII^o.

Chord functions in the key of C major

C     D     E     F     G     A     B - C major scale
|     |     |     |     |     |     |
C     Dm    Em    F     G     Am    B^o - Chord Name
I     IIm*  IIIm  IV    V     VIm   VII^{o - Function}

*Traditional classical theory uses a lower case Roman numeral to indicate a minor chord function....ii, iii, vi. And the small m is not used. It more modern theory...Jazz, Rock, and other contemporary music, chord functions use capital Roman numerals. Then a small m is used if the chord is minor, a small circle is used for diminished, and there are other modifiers as well that will tell you what the quality of the chord is. (Ex. IIm, IIsus2, II7)

The harmonization (creation of chords or harmony) of a major scale will always follow the same pattern, no matter what major key you are in. The chord build from the first degree of the scale is always major. The chord build from the 2nd degree is always minor, etc.

Chord functions in all major keys

Page 1, basic chord construction

Page 3, The chords in all of the major keys