Relationship of keys
Music Theory

Relationship of keys

How to determine the set of keys that are most often used when composing songs?

In this article, let’s talk about the  relationship of keys . In general, all major and minor keys form groups of keys that are in harmonic relationship.

Relationship of keys

Consider the key of C major:


Figure 1. Key in C major

In the diagram, Roman numerals indicate the steps of tonality. On these steps, we will build triads so as not to use accidentals , since C-dur has no accidentals:

Triads on Cdur steps

Figure 2. Triads in C major scales

On the 7th step, it is impossible to build neither a major nor a minor triad without accidentals. Let’s take a closer look at what triads we have built:

  • C-major on the I step.
  • F-major on the IV step. This tonality is built on the main step (IV).
  • G major on the 5th degree. This tonality is built on the main step (V).
  • A-minor on the VI step. This key is parallel to C major.
  • D minor on the second step. Parallel key in F-major, built on the IV (main) step.
  • E-minor at the III step. Parallel key in G major, built on the V (main) degree.
  • In the harmonic major, the fourth step will be F-minor.

These keys are called cognate to C major (not including, of course, C major itself, with which we started the list). Thus, related keys are called those keys, the triads of which are on the steps of the original key. Each key has 6 related keys.

For A minor, you can try to find related ones yourself. This should look like this:

  • on the main steps: D-minor (IV step) and E-minor (V step);
  • parallel to the main key: C-major (III degree);
  • parallel to the keys of the main steps: F-major (VI step) and G-major (VII step);
  • tonality of the major dominant: E-major (V degree in the harmonic minor). Here we explain that it is the harmonic minor that is being considered, in which the VII step is raised (in A minor it is the note Sol). Therefore, it will turn out to be E-major, and not E-minor. Similarly, in the example with C-major, we got both F-major (in natural major) and F-minor (in harmonic major) on the IV step.

The triads that you and I got on the steps of the main keys are tonic triads of related keys.


You got acquainted with the concept of related keys and learned how to define them.

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