Old Music Theory

Two keys are relative to each other under the following conditions:

1. When the key signature is the same for the both keys.
2. When the key signature only differs more or less by one accidental, even if the two keys actually differ by more than one accidental in the actual constitution of their scale.

First Class Relative Keys are those which actually only differ by one accidental (either at the clef or in the constitution of their scale.) Examples:

• C major and A minor
• D major and G minor
• F major and C major

Second Class Relative Keys are keys which differ by more than one accidental, i.e. the other keys. Examples:

• C major and D minor – the latter containing a B♭ and C#.
• A minor and E minor – these differ by 3 accidentals. A minor having G# which doesn’t belong to E minor, and the latter has F# and D#.

Each major key has five relative keys, three are first class, the other two are second class.

Example for C Major:

First Class Relative Keys of C Major:

• A minor
• G major
• F major

Second Class Relative Keys of C Major:

• D minor
• E minor

Each minor key also has five relative keys. One is first class, the rest are second class.

Example for A minor:

First Class Relative Key of A minor:

• C major

Second Class Relative Keys of A minor:

• G major
• F major
• E minor
• D minor

Here is a quick mnemonic:

You’ll find the relative keys of any major key starting form the tonic of the key and rising from degree to degree to the sixth.

You’ll find the relative keys of any minor key starting form the tonic of the key and descending from degree to degree to the third (albeit modifying the 7th degree).

In short, go up by six degrees for the major mode, go down six degrees for the minor mode.