In our previous posts, we introduced the seven musical modes—Ionian, Dorian, Phrygian, Lydian, Mixolydian, Aeolian, and Locrian.
In this article, let’s talk about the key signatures of the various modes.
Key Signature for Major and minor keys
A particular key signature is commonly associated with the major and its relative minor key.
For example, below is the key signature of E Major, and its relative minor, C minor:
Now that we have learned the 7 different modes, we know that Major keys are Ionian mode, and Minor Keys are Aeolian modes. If we already know how to derive the key signatures for the Major keys and the minor keys, then we can use this as reference to determine the key signatures of other keys.
Using Ionian mode (Major) and Aeolian mode (Natural minor) as example
Let’s go back to a simple and familiar example: C major. It has no sharps or flats in its key signature. The relative minor of C major is A minor, because A is the 6th degree of the C major scale. If we extend this concept, we will be able to find all the different modes that share the same key signature as C Major.
In C Major, the notes in the scales are: C-D-E-F-G-A-B-C, so C Major (or C Ionian), D Dorian, E, Phrygian, F Lydian, G Mixolydian, A Aeolian (or A minor) and B Locrian all share the same key signatures. Each of these modes uses only the notes from the C major scale, so they all have the same key signature: no sharps or flats.
This concept applies to any major scale. If you know the key signature of a major scale, you automatically know the key signature of all its modes. The only thing that differs for C Major, A minor, D Dorian, etc. is the tonal center—the note that feels like the starting point.
What’s Next?
Now that we’ve explored all the modes derived from the C major scale, try applying the same process using other major scales as your starting point. Pick any major key, identify its key signature, and then build the seven modes by starting on each scale degree. You’ll find that all seven modes will share the same key signature as the original major scale, just like they did with C major.
Understanding modes is really about seeing the same collection of notes from different “starting points”. By knowing that all the modes of a given major scale share the same key signature, you can quickly identify or write modal music.