Understanding the relationship between keys, scales, and chords

Question

Each song is played in ONE specific key. I am under the assumption (according to the circle of 5ths) there are 24 keys (where each key has a combination of sharps or a combination of flats).

What I am confused on is how does a key relate to a specific scale? So if you are in the C major key (with no sharps or flats) you can play the C major scale, C Natural Minor scale, and C Melodic Minor scale. But the C natural minor scale has a Eb in it even though the C major key has no sharps or flats?

Are a key and scale even related to one another?

Answer 1

Are a key and scale even related to one another?

Of course they are. They're even almost the same thing. What you seem to be missing is that C major is a different key that C minor. C major truly has no sharps or flats, but C minor has 3 flats (B flat, E flat, A flat). There goes your E flat. (Also your 24 keys = 12 minor + 12 major. Although there are loads of other possible keys and modes.)

And, by the way, this proposition

Each song is played in ONE specific key.

is very far from true. In one piece, you can be moving from one key to another (it's called modulation and it's pretty common thing to do). As a classical music enthusiast I won't be able to give examples from popular music, but others surely will.

Answer 2

Well, you're right about the 24 keys (sort of). There's a major and minor key based on each note of the chromatic scale. From then on, I'm afraid you're floundering. A key and its associated scale is a framework, not a strait-jacket. It's the black-and-white drawing, waiting to have colour applied.

Actually, that's quite a nice analogy. Stick to the notes of the major scale, black-and-white drawing. That's fine, but simplistic. But it can be coloured in! Make the sky blue and the grass green, all the expected colours, you've got Common Practice tonal harmony. Make the sky magenta, the people orange, we're getting into advanced chromaticism (or, coming from another angle, jazz substitutions) but we still mostly see what everything's meant to be. Colour OUTSIDE the lines, or take the lines away altogether, we're into atonality (or free-form jazz...)

This may not mean much to the questioner, who seems to be just dipping his toes into understanding music. But, even if you're a guitarist, with no ambitions beyond jazz or rock improvisation, just dial up a bit of Mozart, Beethoven, Stravinskey, Miles Davis... All this is available to YOU too!

Answer 3

Well, it's not quite true to say "Each song is played in ONE specific key". It's not at all unusual for a tune to temporarily change to a different key, and a lot of pop songs change key towards the end and then stay in the new key.

Next, a key isn't really a combination of sharps and flats. Rather, it's a starting note and a scale built on that note. C major and A (natural) minor have the same set of sharps and flats (none!), but are different "keys". Because you are starting on different notes, the pattern of tones and semitones is different so the scale is different.

If you got to 24 keys because of 12 minor and 12 major keys, you have a whole world of modes yet to discover. Using just the white notes on a piano - no sharps or flats - you don't have to start on C (for major) or A (for natural minor). There are seven notes you can start on, each giving you a different scale, and each with its own name. Starting on D (which gives you a key called the Dorian) or G (Mixolydian) is common in Western folk music. Other starting places have other uses. And that's before we even start thinking about different patterns of intervals in the scale, such as we might find in jazz or world music (and the melodic minor, which "tweaks" the natural minor for musical convenience). It doesn't help that people tend to be sloppy with naming, and say a piece in D Dorian is in C just because it has no sharps or flats.

I think that's where your problem with the C natural minor comes from. If you start on A - not C - with no sharps or flats, you get a natural minor scale, but it's A natural minor, not C natural minor. To get to C natural minor, you have to shift the pattern of tones and semitones to start on C, not A. It turns out that gives you the same notes - the same set of flats - as Eb major. It's not Eb major, though, because the tonal centre is C.

So the answer to "are a key and scale even related to one another?" is yes, they are, but it's very far from a simple one-to-one relationship.