The Complete Idiot''s Guide to Music Theory

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Let’s use the key of C as an example, because it’s made up of only the white

keys on a piano. When you play a triad based on C (the tonic of the scale), you

play C E G—a C Major chord. Now move up one key, and play the next

triad—D F A, or D minor. Move up another key, and you play E G B, the E

minor chord. Move up yet another key, and you play F A C—F Major. Keep

moving up the scale and you play G Major, A minor, and B diminished. Then

you’re back on C, and ready to start all over again.

This type of chord building based on the notes of a scale is important, because

we use the position within a scale to describe the individual chords in our

chord progressions. In particular, we use Roman numerals (I through VII) to

describe where each chord falls in the underlying scale. Uppercase Roman

numerals are used for major chords; lowercase Roman numerals are used for

minor chords. To indicate a diminished chord, you use the lowercase Roman

numeral plus a small circle. To indicate an augmented chord, use the uppercase

Roman numeral plus a small plus sign.

Thus, within a major scale, the seven chords are notated as follows:

I ii iii IV V vi vii°

If you remember back to Chapter 2, each degree of the scale has a particular

name—tonic, dominant, and so on. We can assign these names to the different

chords, like this:

I ii iii IV V vi vii°

Tonic Supertonic Mediant Subdominant Dominant Submediant Leading Tone

Of these chords, the primary chords—the ones with the most weight—are the I, IV,

and V. These also are the only major chords in the major scale—and often the

only chords used within a song.

When describing chord progressions, we’ll refer to chords by either their

Roman numerals or their theoretical names (tonic, dominant, and so forth).

You can figure out which specific chords (C Major, D minor, and so forth) to

play, based on the designated key signature.

To make things easier, you can refer to the following table, which lists the

seven scale-based chords for each major key signature.

Scale-Based Chords

Key Signature Chords

C

C