Music Theory Basics

Each major key consists of 7 chords as follows. We will use capital roman numerals to denote major chords and lower case to denote minor.

I - ii - iii(don't use this) - IV - V/V7 - vi - vii(diminished)/vii(diminished) 7

Each chord serves one of three functions: tonic, subdominant or dominant. A typical musical phrase starts in tonic, move to subdominant then to dominant, then back to tonic again. You can also move from subdominant back to tonic, but never from dominant back to subdominant. A phase ends with a cadence, when a dominant chords moves to a tonic chord.

Tonic Chords

In a major key, the chord that most commonly serves the tonic function is the I chord. A vi chord can be substituted occasionally when coming from a dominant chord or used to expand I. This chord progression( V-vi) is called a deceptive cadence and is used to extend a phrase. Almost all phrases however, start and end on a I chord.

Subdominant Chords

ii and IV are subdominant chords, with IV being the most common. Subdominant chords are used to develop a phrase, and bridge the gap between the tonic and the dominant sections. Once we move from tonic to a IV chord, we can go back to tonic if desired. However, it is very rare to go from a ii chord back to tonic. Moving from IV to ii is ok, and is often used to expand the subdominant but ii to IV is not.

Dominant Chords

V and vii are dominant chords. Take note that vii is a diminshed chord, meaning it is very dissonant, so use it sparingly. It is common to use a V7 or vii7 instead of V or vii, and it is also common to move from V-V7. Once a phrase reaches the dominant section, it must resolve to tonic, either to a vi chord(deceptive cadence) or a I chord(authentic cadence).

Some Common Chord Progressions

I-IV-V(7)-I

I-IV-ii-V(7)-I

I-IV-vii(7)-I

I-IV-I-ii-V(7)-I

I-IV-V-vi-V(7)-I

I-vi-IV-ii-vii(7)-I

I-IV-V(7)-vi-I-IV-V(7)-I