Keys and Key Signatures

1. What is a Key?

A key is a system where notes are organized around a central tone called the tonic, and it plays an important role in determining the direction of melody and harmony.

While a scale is simply a sequence of notes following a certain pattern, a key assigns each note a specific function and role within the system. The notes in a key interact with one another to create a sense of tension and resolution, which guides the flow and structure of the music.

2. Primary Tones in a Key

The three most important tones in a key are:

• Tonic: The central tone of the key, offering the most sense of stability.
• Dominant: Located a perfect fifth above the tonic, it naturally resolves to the tonic and adds tension to the music.
• Subdominant: A perfect fourth above the tonic, often serving as a bridge toward the dominant.

Music tends to flow naturally when built around these three tones. Other tones in the key, such as the leading tone, also contribute to the harmonic flow with their specific functions.

The beautiful harmonies we hear in everyday music are created through smooth progressions between chords based on these primary tones (tonic chord, dominant chord, subdominant chord, etc.).

Names of each note in a key (e.g., C Major Key)

3. Diatonic Chords

Diatonic chords are built by stacking thirds on each scale degree within a key, forming triads or seventh chords.

For example, in the key of C Major, there are seven basic chords built on the notes C, D, E, F, G, A, and B: CM7, Dm7, Em7, F7, G7, Am7, Bm7♭5. These chords can also be notated by their position in the key as IM7, IIm7, IIIm7, IV7, V7, VIm7, and VIIm7♭5.

Because diatonic chords are made up entirely of notes within the key, they sound stable and strongly express the character of the key.

4. Key Signatures

So far, we've only looked at C Major (with C as the tonic), but other white keys like D, E, F and black keys like E♭ or A♭ can also serve as tonics.

To represent major keys starting on notes other than C, we use key signatures. A key signature consists of sharps (♯) or flats (♭) placed after the clef to indicate which notes are to be consistently raised or lowered throughout the piece.

As we learned in the Scale section, the major scale follows a pattern of whole-whole-half-whole-whole-whole-half steps. Since major keys are built on major scales, they follow this exact structure.

Let’s take G Major as an example. G Major is a major key with G as its tonic. Listing seven consecutive notes starting from G:

G Mixolydian Scale Sheet

In a major scale, the 6th and 7th notes must be a whole step apart, and the 7th to the tonic must be a half step. But in the example, the interval from the 6th to the 7th is a half step, and from the 7th to the tonic is a whole step.

To fix this and match the major scale structure, we raise the 7th note (F) by a half step to F♯, restoring the correct pattern.

G Major Scale Sheet with accidental

Therefore, the note F must always be raised to F♯ in G Major. Instead of using accidentals throughout the piece, we can use a key signature.

G Major Scale Sheet with key signature

You can see a ♯ symbol on the F line right next to the treble clef. This means that all F notes, regardless of octave, are to be played as F♯ throughout the piece.

To further aid understanding, let’s look at another example — F Major.

F Lydian Scale Sheet

This scale starts from F and lists seven consecutive notes. The pattern turns out to be whole-whole-whole-half-whole-whole-half, which is not the major scale structure. By lowering the 4th note (B) by a half step to B♭, we restore the correct pattern.

F Major Scale Sheet with accidental

This can also be notated using a key signature.

F Major Scale Sheet with key signature

You’ll see a ♭ symbol on the B line right next to the clef. This means that all B notes in the piece must be played as B♭ regardless of octave.

In this way, key signatures allow us to clearly express all major and minor keys. (We'll study minor keys later.)

5. Summary

In this section, we explored the concept of keys, major scales, and key signatures. Now try selecting a tonic to view the corresponding key signature and diatonic chords — and hear how they sound!

Good to know

Order of Sharps and Flats

Sharps (♯) are added in the following order: F, C, G, D, A, E, B.

Flats (♭) are added in the reverse order: B, E, A, D, G, C, F.

These orders are based on perfect fifths — one of the most stable and harmonically rich intervals in music.

Sharps are added upward in perfect fifth intervals. For example, starting from C Major, go up a perfect fifth to get G Major, which adds F♯. Then from G, go up a perfect fifth to D Major, which adds C♯, and so on.

Flats are added downward in perfect fifth intervals. From C Major, go down a perfect fifth to get F Major, which adds B♭.

This system works because it allows the construction of new major scales with minimal change by moving in fifths.

This logic is visualized in the Circle of Fifths — a powerful tool in understanding key relationships and reading music.

The Circle of Fifths — a visual summary of keys and key signatures