Why are Ionian and Aeolian considered Major and Minor keys respectively, but not the other modes?

Question

Why is the Ionian mode called a major key, and the Aeolian mode called a minor key, while the other modes aren't called "Keys"?

F Major is relative to D Minor, and just so G Dorian is relative to both, yet G Dorian isn't given the same privilege of being called a key.

Would it not make it easier to understand/teach the relation of the Modes to each other if the other modes were called by key relativity? (F Major, G Dorian, A Phrygian, Bb Lydian, C Mixolydian, D Aeolian, E Locrian) This way, I would think, it would be easier to relate the modes to the key signatures on sheet music.

As a suggested naming convention, couldn't we call Dorian "Super Key", Phrygian "Mediant Key", Lydian "Subdominant Key", Mixolydian "Dominant Key", Aeolian "Minor/Submediant Key", Locrian "Leading Key"?

Answer 1

Firstly, let's separate the idea of a mode an a scale. Here's an existing question: What is the difference between a mode and a scale?

Each scale has a set of modes. You could visualise a scale as a set of notes in an order, but without a starting point. Most of the time you just start at the "first" note, which gives you the first mode. So we tend to mean "the first mode of the major scale" when we say "major scale". A shortcut, if you will, but generally not a problem.

If we mean "natural minor scale" when we say "minor scale", the same applies to the minor scales as well. If we use a different minor scale, you actually end up with a whole different set of modes, but let's not go there at the moment.

So it's not that Ionian and Aeolian are some special modes with naming right sponsorship over the scales. They just happen to be the names of the mode starting on the first note of a scale. Which are by far the most common modes in Western music. But far from the only ones.

I'm not sure I understand the benefits of your suggested naming convention. Sure, the existing names seem a bit arbitrary. All names are, when you get down to it. It's just part of the language of music. But let's consider the proposed names.

Take Mixolydian. Sure, it's built on the fifth note of the scale. But I don't think calling it "dominant" is helpful. The first chord (a major triad built on the fifth note of the scale) would have tonic function. It'd be better to just label the modes using numbers. But that won't happen, because of historical inertia. And also Mixolydian sounds cooler.

An aside: I've heard Ionian, Lydian and Mixolydian referred to as "major modes", and Dorian, Phrygian and Aeolian called "minor modes". That's basically because they have major and minor thirds, respectively. I guess that makes Locrian a diminished mode, but tonicising a diminished chord is a little challenging, so it's not as commonly used. I don't think that's part of your question, but it's another way that "major" and "minor" get thrown around when it comes to modes.

Answer 2

From your question, it looks like you're thinking about it this way: that there's the underlying diatonic scale, and then the 7 modes are derived from starting at different points on that, giving us Ionian, Dorian, Phrygian, Lydian, Mixolydian, Aeolian and Locrian. You're then asking why only two of those modes have been given special names ('Major') and ('Minor') with the 'right' to denote keys, which is a perfectly reasonable thing to wonder!

It seems that one relevant thing to bear in mind is the way the word 'mode' has been used to refer to lots of different things over the years - The Wikipedia article on modes makes that clear, as do answers on another question from Robert Fink and David Utzinger.

Christopher Whitt highlights the point at which the idea of major and minor came into the mix:

The next milepost in the misnaming of church modes happened over a 75 to 100 year period ending in roughly 1675 ... when the church modes of Gregory were expressed as permutations of the then new major-minor scale system. That's when the modes became formalized into what we know and use today. The Greek names became convenient labels for particular scales, though there is no certain tie between the notes in any modern church mode and the notes in any ancient Greek mode. Locrian mode was 'invented' to complete a theoretical picture.

Caleb Hines has written an informative question (and answer!) on how the major / minor system slowly came to be established. once it was, it seems that the word 'mode' was then re-used yet again to mean another new thing - 'mode' of the major scale. So that seems to be why in the current, modern definition of mode, the Major/Minor system is seen as the 'parent' concept, and the modern modes are seen as a secondary concept that's derived from that.

However, in the past, the word 'mode' has been used to refer to different concepts that were perhaps more on the same primary level of importance as our modern 'keys' - some of which themselves fed into the development of the major/minor system.

Music is full of terms that mean more than one thing in different contexts - sometimes contexts do make that clear, but some musical ideas just seem to be problematic, and the idea of 'modes' seems to be one of those. Again from Caleb's answer:

Throughout the Baroque, there seems to have been widespread confusion, even among musicians, over the exact definition of a mode.

...and this gem from the Wikipedia answer:

The understanding of mode today does often not reflect that it is made of different concepts which cannot fit altogether.

Answer 3

Basically, naming conventions are pretty arbitrary and historically, not logically, evolved. Imho, "major" and "minor" as opposed to "modes" is not-so-simply the result of European "art" music settling on the Church (as opposed to Greek) modes of Ionian ("major") and Aeolian ("minor", when aided and abetted by #7 and #6) as the basis of "functional harmony".