1.5 Major keys and key signatures

1.5 Major keys and key signatures

A key signature tells you which pitches belong to a scale, but it does not by itself tell you whether the music is major or minor. The decisive clue is the central pitch—the pitch that sounds like “home.”

PIT-1.F.1: When a particular major or minor scale is used prominently and its tonic is established as the central pitch, the music is said to be in the corresponding key.

For example, a passage may use the pitches of the D major scale and repeatedly emphasize $D$ through melody, harmony, or cadence. Because $D$ functions as the tonal center, the passage is in the key of D major.

Key, scale, and key signature

A scale is an ordered collection of pitches. A key is the tonal organization created when one pitch—the tonic, or central pitch—acts as the point of rest. A key signature is the grouping of sharps or flats placed after the clef that represents the pitch collection associated with a major or minor key.

In D major, the scale is:

$$D\ E\ F\sharp\ G\ A\ B\ C\sharp\ D$$

The key signature contains two sharps, $F\sharp$ and $C\sharp$. Once those sharps appear in the signature, every $F$ and $C$ is normally performed as sharp unless an accidental temporarily changes it.

Pitches belonging to the prevailing scale are diatonic. A pitch outside that scale is chromatic. Thus, $F\sharp$ is diatonic in D major, while $F\natural$ is chromatic unless the music changes its tonal context.

Major and minor can share a key signature

A major key and a minor key may use the same key signature. D major and B minor are a crucial example:

Tonal collection	Pitches	Key signature
D major	$D\ E\ F\sharp\ G\ A\ B\ C\sharp$	$F\sharp$, $C\sharp$
B natural minor	$B\ C\sharp\ D\ E\ F\sharp\ G\ A$	$F\sharp$, $C\sharp$

The shared signature represents the natural-minor collection for B minor. Minor music may then alter pitches with accidentals. In B harmonic minor, the seventh scale degree $A$ is raised to $A\sharp$:

$$B\ C\sharp\ D\ E\ F\sharp\ G\ A\sharp\ B$$

In ascending B melodic minor, the sixth and seventh degrees are raised:

$$B\ C\sharp\ D\ E\ F\sharp\ G\sharp\ A\sharp\ B$$

The raised $G\sharp$ and $A\sharp$ are written as accidentals in the music; they are not added to the ordinary B-minor key signature. This distinction matters: the key signature identifies the underlying collection, while accidentals show temporary alterations such as harmonic- or melodic-minor inflections.

Identifying a key signature in notation

Read a key signature in two stages:

1. Identify the sharps or flats and their order.
2. Decide which pitch acts as tonic.

For sharp signatures, the last sharp is usually one half step below the major tonic. If the signature contains $F\sharp$ and $C\sharp$, the last sharp is $C\sharp$; one half step above it is $D$. The major key is therefore D major.

For flat signatures, the major tonic is generally the second-to-last flat. For example, a signature containing $B\flat$, $E\flat$, and $A\flat$ points to E-flat major, because $E\flat$ is the second-to-last flat. The one-flat signature is the exception: it identifies F major.

The clef changes where the symbols appear on the staff, but not what they mean. In treble clef, a key signature containing $F\sharp$ and $C\sharp$ still means those pitch classes are sharp; in bass clef, the symbols are positioned differently but identify the same signature.

Major or relative minor?

When a key signature could represent either a major or minor key, inspect the musical evidence. Look for the final or longest-held pitch, repeated emphasis, melodic arrival points, and harmonic cadences. A signature of two sharps may indicate D major if $D$ feels like home, or B minor if $B$ is the tonal center.

Common misconception: “The key signature tells me the key automatically.”
A key signature tells you the available default pitches, not necessarily the tonic. The same two-sharp signature can belong to D major or B minor; tonal center determines the answer.

Common misconception: “A raised seventh changes the key signature.”
In minor music, a raised seventh such as $A\sharp$ in B harmonic minor is normally written as an accidental. It changes the pitch used at that moment, not the underlying key signature.

Worked identification

Suppose a bass-clef melody has two sharps in its key signature, repeatedly ends on $B$, and uses $A\sharp$ before the final $B$. The reasoning is:

• Two sharps establish the shared D-major/B-minor pitch collection.
• The repeated arrival on $B$ identifies $B$ as the tonal center.
• The $A\sharp$ is a raised seventh, supporting harmonic minor.
• Therefore, the passage is in B minor, not D major.

Retrieval check: A treble-clef passage has three flats, repeatedly rests on $C$, and cadences to $C$. Is it C minor or E-flat major? What evidence would confirm your answer, and which pitch alterations might appear in C harmonic or melodic minor?