Is there a set of closely related keys in modern popular music?

Question

In my knowledge, the closely related keys in classical music are: In C-major: 1. C-major (Tonic, original) `♮` 2. d-minor (Supertonic, relative of subdominant) `♭` 3. e-minor (Mediant, relative of dominant) `♯` 4. F-major (Subdominant) `♭` 5. G-major (Dominant) `♯` 6. a-minor (Submediant, relative) `♮` 7. e-minor or G-major (b-diminished is not a key) `♯` In a-minor: 1. a-minor (Tonic, original) `♮` 2. e-minor or G-major (b-diminished is not a key) `♭` 3. C-major (Mediant, relative) `♮` 4. d-minor (Subdominant) `♭` 5. e-minor (Dominant) `♯` 6. F-major (Submediant, relative of subdominant) `♭` 7. G-major (Dominant, relative of dominant) `♯` Is there a set of closely related keys in modern popular music? If yes, then what will it be?

Answer 1

If I understand your question correctly, you are asking if there are closely-related keys in modern popular music in the same fashion as classical music. The short answer is yes - all closely-related keys are available in modern popular, classical, jazz, and every other Western music genre that is currently in existence. So, if you find a closely-related key set in Western classical, it will also prove to be in existence in Western popular.

Additionally, you do not have to start at C to find closely-related keys (this may have been an example on your part); any note will work to perform the same functions (Bb / A#, Fb / E, Cb and B, etc.) - the only real difference between them is the spelling of the note (A# vs Bb, Fb vs E) and their respective function placements.

There are also modes (C major scale is also C Ionian mode; A minor scale is also A aeolian) which can be built in the same way off of any 'home' key. This point is more toward your comment that there is no b-diminished scale; while true, there is a B Locrean scale, which reads in steps as Half-Whole-W-H-W-W-W. Depending on the intent, mood, style, and composition of the music, any key works as a closely-related cousin to any other key in Western music!

I hope this helps! Please feel free to add a comment if you would like more information or would like to clarify anything.

Answer 2

Your examples here point more specifically in the direction of FUNCTION and MODE, rather than simply "related".

Function

Tonic, Supertonic, Mediant, etc are FUNCTIONS that a chord may serve relative to the key in which it is performed. As in, for example C-major: the FUNCTION of a C chord (Tonic) is to establish a "home base" for the harmony to depart from or return to. The function of the Dominant (G major) is to give the strongest desire to return to the tonic (it dominates the harmony). The mediant and submediant tend to be "softer" extensions of the tonic harmony that don't particularly point in any direction unless they're preceded or succeed by a chord with more clear direction.

Mode

Mode could be thought of in a few way, mainly these two:

1. Keep the key signature, move the tonic: for example same key signature as F major (one flat), but "home base" could be G, which in this key would make a Tonic chord a G-minor (G Bb D). All music motion would use that G-minor chord as it's point of reference to which it would return to at the close of the musical passage. In this case, the piece would be in G Dorian.
2. Keep the tonic, move the key signature: now let's keep C as our Tonic but use a different key signature, two flats (same as B-flat major), only now I have an altered 3rd and 7th scale degree. now a C chord plays a tonic role because it references our "key center" but will sound more like the key C-minor. In THIS case, we're in C Dorian.

I hope that helps! Let me know!