This is the third part in my series about music theory. In the previous post, we covered musical scales, namely the Major and Natural Minor scales. In this part, we'll cover key.

Remember: You can hit the notes to play their sounds. If you're on iPhone, turn your ringer on to enable sound.

Scales Share Notes

Recall that a scale is no more than a group of notes within the same octave. The notes, or degrees, in a scale are typically found by starting at the root note (often called the tonic) and moving along a sequence of whole and half steps.

An interesting phenomenon related to scales is that the notes in their degrees aren't unique to the scale. For example, here's the C Major scale.

C
C#
D
D#
E
F
F#
G
G#
A
A#
B
C

And here's the A (Natural) Minor Scale.

A
A#
B
C
C#
D
D#
E
F
F#
G
G#
A

And if we shift the above keyboard to the left a few keys we get...

C
C#
D
D#
E
F
F#
G
G#
A
A#
B
C

Woah! The C Major and A Minor scales both have all notes of the white keys in their scale. Does this mean that they're identical?

Not necessarily. The notes of their degrees still differ. For example, the second degree of the A Minor scale is B, while the second degree of the C Major scale is D.

Key

In most Western music, a sequence of notes like that of a melody or entire song typically starts from and returns to the tonic of a scale. If this is the case, the sequence is known to be in the key of the scale of which that note is the tonic. For example, the song "Mary Had a Little Lamb" is often played in the key of C Major.

This is because the melody of the song uses notes from the C Major Scale and feels resolved or closed when the C note is played.

Here, you can see that "his fleece was white as snow" ends on a C and sounds like this.

The melody felt finished, or resolved, on that C note. To be sure of this, let's remove that last C and see how the melody sounds.

It's a bit unsettling, right? You know that there's a note that would provide a satisfying finish to the above melody, but it's just not there.

That note is the tonic, or C in this case.

Finding the Key of a Song

Put simply, key is a scale plus a tonic. So, we can find the key that a song is in by first finding the scale. We need to ask ourselves what notes are being played throughout the song, then what scales encapsulate those notes.

In the case of "Mary Had a Little Lamb", the notes in the song are on some of the white keys of a piano. This means that two possible scales for this song are A Natural Minor and C Major, since those two have all white keys in their scale.

Then, we need to listen to the song and determine when resolutions occur and on which note those resolutions take place. Once you've found that note, find out which one of the scales from earlier has that note as its tonic. The key of the song is named after that scale.

As we can recall from earlier, "Mary Had a Little Lamb" resolves on a C. A C is the tonic of C Major and not A Natural Minor, so this song is in the key of C Major!

FAQs

Why don't I always hear people say that the key of a song is in X Major?

When a key is in a major scale, people will typically leave out the "major" part when referring to it. So, when people say that a song is in the key of A, for example, they're saying that the key is in A Major.

Do major and minor keys have the same tonic?

Yes, just like how the E Major and E Minor scales, for example, have an E note as their first degree, keys in E Major and E Minor both have E as their tonic.

What's next?

In the next post, we'll cover chords.

Additional Resources

What is a key? - Dave Conservatoire (YouTube)