Sus4

Sus4, short for "suspended fourth," is a type of chord commonly used in music theory and practice. It is characterized by the replacement of the third component of a major or minor chord with a perfect fourth interval above the root. This creates a sense of suspension or expectancy, as the chord lacks the stable major or minor third that defines its quality.

Typically, a sus4 chord is built by taking the root note, the perfect fourth, and the perfect fifth of a scale or chord. For example, a Csus4 would consist of the notes C, F, and G. The resulting chord creates a sound that is open and unresolved, often used to create tension that can be resolved by returning to a major or minor chord.

Sus4 chords are used across many musical genres and are frequently found in progressions to add harmonic interest and suspense. They can be played as triads or extended with additional notes, and are often used as passing chords or to emphasize transitions within a piece.

In notation, sus4 chords are typically written with the "sus4" designation after the root letter or number (e.g., Csus4, D7sus4). The suspended fourth can sometimes also be notated as "sus" alone when the context makes the chord's quality clear.

While sus4 chords are versatile and widely used, their defining feature remains the inclusion of the perfect fourth, creating an ambiguous or suspended quality that can be resolved for harmonic stability or tension. Their role enhances melodic motion and emotional expression in various musical compositions.

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