Musical scales, keys and modes explained


Category: technical

I was going to write exclusively about modes, but given the impenetrable definitions on the web a more comprehensive post seems in order. (I'd title it Music Theory For Dummies but it doesn't cover rhythm, tempo, dynamics and all that goodness.)

In order to understand modes, you need know a few other things first, starting with...


Like light, sound comes in a spectrum. If you start at one end and go towards the other, you'll see the frequency change gradually. What you hear at any given point (ignoring the loudness) is the pitch. With the light spectrum we like to divide it up into manageable chunks: this range of frequencies we'll call 'red', that bit 'blue', and so on. But how do you describe pitch? Say hello to the...


Just as the light spectrum has 'colours', the sound spectrum has 'notes'. The thing is, people very rarely compose music with all the notes available to them. Dump all the notes into a piece and it'll sound more like noise than music. Think of it this way: do painters paint every picture with every colour imaginable? No, they limit themselves to a palette. Similarly, composers have the...


(Finally!) A scale is a collection of notes ordered by pitch. For reasons unknown, the distance between two adjacent notes is known as a 'semitone' and two semitones make up a 'tone'. The previously mentioned 'all the notes' scale for example, is called the 'chromatic scale' and consists of 12 consecutive notes (N = note, - = semitone):


But hardly anyone uses that scale in real life. The scale we are most familiar with is called the 'diatonic scale'. It goes like this:


See that pattern? Two tones, then a semitone, then three tones, then a semitone, then two tones... Now if you were to sit at a piano, pick a random note and apply that pattern (counting both black and white keys as notes) up to 8 notes, what you get is a 'major scale'. If you start with a C, it just so happens that you can play a major scale without touching any black keys; the piano was designed with the diatonic scale in mind. Another cool thing about major scales is that the notes at each end sound very similar - so similar, in fact, that we gave them the same name! If a major scale starts on a C, it ends on a C and the cycle starts again:



When people say "that song is in the key of A major", what they really mean is that it uses a major scale whose first note is A, that is, the A major scale. The note intervals are exactly the same as those in the C major scale, which starts on C naturally. Same for every other major scale. As a result they all sound kind of similar to our ears - bright and happy. But what about minor keys? We'll get to those in a bit.


Musical modes may seem like an esoteric concept, but they're really just different ways of using the familiar diatonic scale. Variations on a scale, if you will. Take the 7-day week for example: I may think the week starts on Monday, but some people think it starts on Sunday, or even Saturday. That's not to say my view is more valid than someone else's, it just means that I'm used to Monday being the First Day of the Week.

Likewise, songs written using the C major scale put a lot of weight on the note C, because that's what we're used to hearing. Either the melody starts with a C, ends with a C, or the C chord figures prominently in the harmonies. It's the tonic - the most important note, the beginning and end - of the C major scale:


What if such a song were to emphasise, say, the second (II) note in the scale instead? It may sound odd to our ears, but it's a perfectly valid way to write music. Then the scale would run from D to D like this:


Note that the intervals (pattern of semitones and tones) haven't changed. We've simply decided to shift the 'tonic' - the most important note of the scale - to D. The new scale still has 8 notes, but sounds different. It's effectively a variation of the C major scale. How about if we shift the tonic to the third (III) note?


Sounds different yet again! We can do this all the way up to C, where it becomes the C major scale again. These 'variations' are what we call 'modes'. Modern western music theory has pretty names for all these modes:

(Using the C major scale as an example.)

Mode I, or the Ionian mode:
C to C in the C major scale
Mode II, or the Dorian mode:
D to D in the C major scale
Mode III, or the Phrygian mode:
E to E in the C major scale
Mode IV, or the Lydian mode:
F to F in the C major scale
Mode V, or the Mixolydian mode:
G to G in the C major scale
Mode VI, or the Aeolian mode:
A to A in the C major scale
Mode VII, or the Locrian mode:
B to B in the C major scale

A 'minor' scale is simply the sixth (or Aeolian) mode of a major scale. So the A minor scale goes from A to A in the C major scale. A song written in the key of A minor uses the same notes as a song written in C major, but its focus is on A instead of C. That's what makes it sound different.

But what about the other keys such as A major and G major and D♭ major? Do they have modes too? Of course. If we do the maths: 12 keys × 7 modes = 84 combinations!

Dorian? Phrygian? What mode is that song in?

Here's how to work out what mode a song is in:

  1. Find the key signature.
  2. Find the major key that has the same key signature.
  3. Find the tonic (where the melody 'comes to rest').
  4. Starting from the tonic of the major key, count upwards until you reach the tonic of the mystery song. That number denotes the mode.

I'll use the Irish folk song My Lagan Love as an example. First I'll play the tune starting from a random note (B♭). Once I've got that down, I'll take note of the sharps and flats I've used: A♭, B♭, D♭, E♭. This pattern corresponds to the key of A♭ major. The tonic of My Lagan Love is E♭, evident in the end of the first verse ("on her hair") and the end of the song ("lord of all"). E♭ is the fifth note of the A♭ major scale, so My Lagan Love is in A♭ Mixolydian mode! Yay.

For the fourth step you could also use the handy reference chart I've drawn up (see image).

The main hurdles in this method are steps 1 and 3. Most songs are easy, though the ambiguous ones can be really tough. Case in point: the Appalachian carol I Wonder As I Wander doesn't resolve to its tonic and has a missing note that could swing either way. Starting on an E, if the missing note is an F, then the song's in C Aeolian mode; if it's an F♯ - G Dorian mode. I'm more inclined to believe it's in Dorian because if you incorporate that missing note into a modified version of the phrase "out under the sky" (A-G-?-E-D), F♯ sounds much more 'natural' than plain F. But that's coming from someone who insisted on playing the Aeolian Greensleeves sheet music in Dorian...

Companion piece alert!

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