A Gentle Introduction to Tonality in Music

Tonality in music refers to melodies and harmonies that revolve around a single note known as the tonic note.

As soon as a song begins, our brain starts to figure out which note is the tonic. The tonic note is the melody’s most important note, representing home, certainty, and resolution. Every other note in the song will, to varying degrees, create tension, uncertainty, and a departure from home.

Before we get into how tonality works in music, let’s define some terms.

Tonal vs Atonal music

There is music in which a tonic note is not established. This is known as atonal music, and it can be found, for example, in the works of Arnold Schoenberg.

Because the human brain craves the concept of home, certainty, or a reference point, atonal music constitutes a very small minority of Western music.

Since a tonic is not established in atonal music, many people, including the author of this article, tend not to like it.

Tonal vs Modal music

Tonal music, also known as Western tonal music, is composed in one of 24 keys, 12 major and 12 minor.

That is, the tonic note can be any of the 12 musical notes, and the key associated with that tonic note can be major or minor.

Modal music functions similarly (a tonic note is established as home), but the associated notes are drawn from a mode other than the major or minor.

Modal music is far less common than tonal music, but it can be found in genres such as jazz and heavy metal. However, modal melodies can be very pleasing to the ear because they adhere to the tonality principle, in which a note is designated as home.

The seven modes of the major scale are known as Ionian, Dorian, Phrygian, Lydian, Mixolydian, Aeolian, and Locrian. The Ionian mode is the major scale, and the Aeolian mode is the minor scale. Thus, the notes in modal music are derived from one of the remaining five modes (or other modes not derived from the major scale).

Despite the fact that modal music is based on the same principles as tonal music, this article will focus on the two types of keys used in the Western tonal system: major and minor.

How tonality in music works

The following short musical example is in the key of C major. 

Three things determine that this piece of music is in the key of C major:

1. The tonic note is C
2. The scale associated with the tonic note is the scale of C major.
3. The chords associated with the tonic are derived from the harmonized C major scale.

Let’s look at these one by one:

1. The tonic note

If you’re writing music in the key of C major or C minor, the note C is the tonic note.

This is the only note in the melody that does not cause unrest, regardless of octave.

The melody above begins on the note C and wanders off to notes that are related (as we’ll see in the next point) but cause dissonance with the tonic (to varying degrees. For example, the note that forms an interval of a perfect fifth from the tonic, G, causes far less unrest than the note that forms an interval of a major second from the tonic, D).

The melody also ends on a long C note that takes up the entire last bar. The melody has arrived home and it’s going to stay there.

2. Scale associated with tonic

What is the difference between C major and C minor if the note C is the tonic in both keys?

The answer is found in the scale associated with the tonic.

If the music is in the key of C major, the related scale is the C major scale, which gives us the note options (C,D,E,F,G,A,B):

If I had chosen to write the music in the key of C minor, the associated scale would be C minor, giving us the following note options (C,D,Eb,F,G,Ab,Bb):

While four notes are the same in the C major and C minor scales, the third, sixth, and seventh degrees of the minor scale are flattened, or played a semitone (one fret on the guitar) lower.

Thus, while music in keys that share the same tonic ends up at the same home (the tonic note), the melody takes a different path.

Only one of these three flattened notes determines whether the key is major or minor. This is the third scale degree note. (Eb in C minor, E in C major)

The reason for this is as follows.

Minor scale variations

The C minor scale given above is also called the C natural minor scale.

The reason is that as tonal music evolved, this scale didn’t satisfy all the needs of composers writing in minor keys since the flattened 7^th degree of the scale (Bb) has a weaker pull towards the tonic than the major 7^th degree (B).

This led to the creation of a variation to the natural minor scale, called the harmonic minor scale.

In the harmonic minor scale, the third and the sixth degree are flattened, as in the natural minor scale, but the 7^th degree is not, as in the major scale (C,D,Eb,F,G,Ab,B):

There is yet another version of the minor scale, the melodic minor.

The third degree is flattened in this scale (otherwise it wouldn’t be a minor scale), but the sixth and seventh degrees are not flattened when ascending (as in the major scale), but are flattened when descending (as in the natural minor scale).

The notes of the C melodic minor scale are as follows: (ascending: C,D,Eb,F,G,A,B; descending: C,Bb, Ab, G,F,Eb, D).

Any of these three variations can be used when writing music in a minor key because the flattened third, which is present in all of them, defines the tonality as minor.

3. Chords derived from the respective scale

To harmonize a scale with chords, take each degree of the scale and stack two intervals of a third on top of each other. This gives us the chords that correspond to each scale degree.

In the key of C major, for example, the tonic note C is harmonized by the first, third, and fifth degrees of the major scale, C, E, and G. These are the notes that make up the C major chord.

In the key of C minor, the tonic is harmonized with the first, flattened third, and fifth degrees of the minor scale, C, Eb, and G. These are the notes that make up the C minor chord. 

The rest of the chords in the scale are harmonized in the same way. In C major, for example, the second degree of the scale is D. This is harmonized by the second, fourth, and sixth degrees of the scale, D, F, and A. These notes form the D minor chord.

If we start with the third degree, E, we get the notes E, G, and B, which form the E minor chord. So on and so forth to harmonize all the notes, which we will cover in greater detail in this lesson.

From one major key to the next, the pattern of harmonized chords is the same:

Major, minor, minor, major, major, minor, diminished.

Thus, if we’re in the key of C major, the associated chords would be:

C major, D minor, E minor, F major, G major, A minor, and B diminished

While if we were in the key of E, some of the chords are different but the chord type pattern remains the same:

E major, F# minor, G# minor, A major, B major, C# minor, and D# diminished.

What about minor keys?

If we had to derive the notes from the natural minor scale, we would get this pattern:

Minor, diminished, major, minor, minor, major, major.

However, due to the existence of the harmonic and melodic minor scale, we can get different chords to harmonize the minor scale.

In fact, there are alternatives for every chord in minor keys, except for the first, which is always a minor triad.

That being said, the harmonic minor scale is the variation of the minor scale from which chords are most commonly derived.

The following is the chord pattern formed by harmonizing the harmonic minor scale:

Minor, diminished, augmented, minor, major, major, diminished.

And this is the ascending melodic minor scale chord pattern (descending it would give us the same chords as the natural minor scale)

Minor, minor, augmented, major, major, diminished, diminished.

The following chart shows you how each note can be harmonized in the minor key.

Remember that if you use notes from any variation of the minor scale, you’re still in the same minor key (ex. C minor).

Chromatic notes and chords

Does playing in a key mean you should never use a note or a chord that isn’t in the key?

No, notes and chords from outside the key are frequently used to add variety to the music.

These are known as chromatic notes (for example, the note F# in the key of C) or chromatic chords (for example, the chord F# major in the key of C).

While these notes and chords can add interest to your music, use them with caution to avoid blurring the tonality. The listener’s brain must know what key you are in at all times or it will feel lost.

Modulation

If you just play the tonic note over again, the listener will obviously get bored. The unrest created by the other notes is what makes the music interesting.

Though (usually) at a slower pace, the chords are also changing, causing unrest with the tonic chord. 

Different notes and chords are enough to provide variety for the listener, but for the more adventurous (and experienced) songwriters, changing key can provide even more variety.

This is known as modulation in music.

Modulation is a fairly advanced topic in music theory and songwriting, and how it is done is beyond the scope of this lesson.

However, keep in mind that the key itself may change during a song.

A songwriter can modulate from any key to another, but the most common modulations are to nearby keys, the ones with the most notes in common.

These are modulations to:

1. The relative major and minor (ex. C major to A minor). These are the closest keys possible since they share the same notes (but a different tonal centre)
2. The key of the fifth degree of the scale (ex: C major and G major). There is only one note different in these keys (F in C major and F# in G major)
3. The relative minor of the fifth degree of the scale (ex: C major and E minor). Because E minor is G major’s relative minor, they share the same notes, so only one note differs from C major. 
4. The key of the fourth degree of the scale (ex: C major and F major). These keys differ by only one note (B in C major and Bb in F major).
5. The relative minor of the fourth degree of the scale (ex: C major and D minor). 

In many cases, the song modulates back to the original key by the end, reinforcing the concept of home once more.

Tonality, unity and variety

Tonality in music is all about giving the listener’s brain what it likes:

1. Enough unity to make sense of what’s going on.
2. Enough variety to make listening to the music enjoyable

Music with too much variety but not enough unity sounds incoherent. Music with a lot of unity but little variety sounds monotonous.

Great composers and songwriters know how to balance the two in ways that pleases the listener.

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