How does one go about finding the relative keys of modes?

For example, determining the relative major of F# Phrygian or determining the relative locrian of G Mixolydian?

  • I would probably first find the tonic in all cases.Seems convenient to me. – alexsms Dec 19 '18 at 7:46

There are a couple of strategies you could use.

  1. Work out the key signature of the starting mode in question & then ascertain the required mode. In your 2 examples, F♯ Phrygian has a key signature of F♯ & C♯, so its relative major is D Major; G Mixolydian has an empty key signature, so the Locrian mode with the same key signature is B Locrian.
  2. Alternatively, use the your knowledge of which scale degrees in the Major scale for the tonics of each mode & work it out from there. You know that the mode mappings on major scale degrees are:

    I   (tonic)        = Major/Ionian
    II  (super-tonic)  = Dorian
    III (mediant)      = Phrygian
    IV  (sub-dominant) = Lydian
    V   (dominant)     = Mixolydian
    VI  (sub-mediant)  = Minor/Aeolian
    VII (leading-note) = Locrian

So in your examples, the Phrygian mode is formed on the mediant (3rd degree) of the major scale, so the "relative major" of F♯ Phrygian is 2 scale steps back in the Phrygian mode (F♯→E→D); the Mixolydian mode is formed on the dominant (5th degree) & the Locrian on the leading-note (7th degree), so the "relative Locrian" of G Mixolydian is 2 scale steps up in the Mixolydian mode (G→A→B).

EDIT: additional answer

A third alternative is to learn the relations between the modes. Just like the relation between the major & relative minor is a 6th, all of the other modes can be related in a similar way. Here's how it would look:

Table interval relations between modes & their relatives
  Read across to the starting mode & down to the relative mode. 
  The resulting interval is the distance between the tonics of the relative modes.

> Starting Mode:     Major | Dorian | Phrygian | Lydian | Mixolyd | Aeolian | Locrian
Relative Major       same  |↓Maj 2nd| ↓Maj 3rd |↓Prf 4th|↓Prf 5th |↓Maj 6th |↓Maj 7th
Relative Dorian    ↑Maj 2nd|  same  | ↓Maj 2nd |↓min 3rd|↓Prf 4th |↓Prf 5th |↓Maj 6th 
Relative Phrygian  ↑Maj 3rd|↑Maj 2nd|   same   |↓min 2nd|↓min 3rd |↓Prf 4th |↓Prf 5th
Relative Lydian    ↑Prf 4th|↑min 3rd| ↑min 2nd |  same  |↓Maj 2nd |↓Maj 3rd |↓Aug 4th
Relative Mixolyd   ↑Prf 5th|↑Prf 4th| ↑min 3rd |↑Maj 2nd|  same   |↓Maj 2nd |↓Maj 3rd
Relative Aeolian   ↑Maj 6th|↑Prf 5th| ↑Prf 4th |↑Maj 3rd|↑Maj 2nd |  same   |↓Maj 2nd 
Relative Locrian   ↑Maj 7th|↑Maj 6th| ↑Prf 5th |↑Aug 4th|↑Maj 3rd |↑Maj 2nd |  same 

So, in your examples we read across to Phrygian in the top line & then down to the Relative Major row & find the interval between the tonics (key-notes) is a Major 3rd, going down for Phrygian to Major. Similarly, Mixolydian to Relative Locrian is up a Major 3rd.

  • Quite helpful. But just wondering does this task often arise in real practice? As a guitar player I find that probably it's practical to view G-Myxolyd. as degree V (dominant) of Cmaj, hence work from Cmaj as basis for all other modes. Or view Fm# as degree III of Dmaj and think of Dmaj as tonal centre (without thinking of key signature, because it's probably not easy to quickly recall that F# Phryg. has two ##s unless one improvises in different Phryg. keys). – alexsms Dec 19 '18 at 7:38
  • @alexsms as a guitar player, I have the same issue. It wouldn't be that easy to recall the number of sharps in different modes – noorav Dec 19 '18 at 7:51
  • 1
    @noorav I also play the piano, so I remember (or can quickly tell, simple methods) all key signatures, but it's usually just the tonic. – alexsms Dec 19 '18 at 7:56
  • @alexsms, I've written up a lookup table for you. I can't think of a way to do this without memorising the relationships. My background being art music, i learned all of these relationships via scales, keys, key signatures & intervals. I can offer no insight into tricks for musicians who don't work with those building blocks as instant recall. – Dean Ransevycz Dec 19 '18 at 8:46
  • @DeanRansevycz, thanks. I guess one could use it too to better remember (understand) some chord substitutions. – alexsms Dec 19 '18 at 8:59

Given that a 'relative key' is another that contains the same notes, as in A minor is 'relative' to C major.

The simplest has to be go to the parent key of the mode. Taking your example of F# Phrygian we go back to parent D major. So 'relative' modes for this example are E Dorian, G Lydian, A Mixolydian, etc. Thus making the relative Locrian to G Mixolydian B Locrian.

Your G Mixolydian example takes us to C major, which gives us D Dorian, E Phrygian, F Lydian, etc.

Knowing key sigs will help with #/b, and it's important to know those anyway.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.