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Key (music)

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In Western tonal music, a key is a system used to organize sounds. It acts as a center of tonal stability for a song or composition. A key is defined by two specific components: a tonic pitch and a mode. The tonic pitch is the primary note that a piece of music revolves around. Most compositions almost always conclude on this specific pitch to create a sense of resolution. The mode refers to the pattern of ascending or descending pitches used in the music. This mode can be Major or Minor. If a mode is not specified, Major is usually implied.

Piano With A Major
Piano With A Major

To understand keys, one must understand the pitches that create them. Music is made of audible vibrations. When a medium vibrates, humans perceive the frequency as a pitch. In Western music, twelve pitch classes are used. Seven of these are natural pitches, represented by the letters A, B, C, D, E, F, and G. The distance between two pitches can be measured in semitones or whole tones. A semitone is the smallest musical distance. A whole tone is a larger distance. On a piano, these distances appear between adjacent keys.

Piano With A Major
Piano With A Major

Scales are the building blocks of keys. A scale is a sequence of seven pitches called diatonic pitches. These pitches are used more frequently than the remaining five chromatic pitches. A Major scale follows a specific pattern of steps: tone, tone, semitone, tone, tone, tone, semitone. An ascending minor scale uses a different pattern: tone, semitone, tone, tone, semitone, tone, tone. This different pattern makes the third, sixth, and seventh pitches one semitone lower than in a Major scale. Because there are twelve possible tonic pitches and two modes, there are 24 distinct keys. For example, C Major and A Minor are distinct keys.

Piano With A Major
Piano With A Major

Musicians use notation to communicate these keys. Music is written on a staff of five parallel lines. A clef defines the relationship between line position and pitch. To represent pitches that fall between natural notes, musicians use accidentals. A sharp (♯) raises a pitch by one semitone. A flat (♭) lowers a pitch by one semitone. A key signature is a shorthand notation placed at the start of a piece. It identifies which pitches are diatonic. This allows the performer to know which accidentals to apply throughout the song. However, a key signature does not specify the tonic pitch.

Piano With A Major
Piano With A Major

Some musical tools require a process called transposition. Transposition involves raising or lowering all pitches by the same number of semitones. Certain instruments, such as the trumpet, clarinet, and saxophone, are called transposing instruments. This means the music written for them is offset from the actual pitch they play. For instance, an E♭ saxophone plays a written C as an E♭. Choosing specific transposing instruments can help simplify a score by reducing the number of accidentals. This makes the written music easier for the performer to read.

When multiple pitches are played at once, they form a chord. A triad is a specific type of chord made of three pitches. Musicians often use numbers to describe these chords to make them easier to move between keys. The Nashville number system uses Arabic numerals for this purpose. In the key of F Major, the root pitch F is numbered 1. The fifth pitch in the scale, C, is numbered 5. Another method uses Roman numerals, where uppercase letters represent major chords and lowercase letters represent minor chords. This allows musicians to analyze common patterns, like the "Doo-wop progression," regardless of the specific key.

Relationships between different keys can be visualized using the Circle of Fifths. This diagram shows how much pitch overlap exists between keys. Keys that are adjacent on the circle share six of their seven diatonic pitches. Moving clockwise around the circle, each key sharpens one pitch. Moving counterclockwise, each key flattens one pitch.

Circle of fifths deluxe 4
Circle of fifths deluxe 4

The diagram also shows relative minors. A relative minor uses the exact same pitches and key signature as a Major key, but it uses a different tonic. For example, A Minor is the relative minor of C Major. When musicians transition smoothly between closely related keys, the process is called modulation.

Circle of fifths deluxe 4
Circle of fifths deluxe 4
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