What defines an authentic cadence in music?

An authentic cadence is characterized by the resolution of a dominant harmony to the tonic. This typically involves a V (dominant) chord resolving to a I (tonic) chord, creating a strong sense of finality and closure in the music. This resolution is fundamental to Western tonal music, as it establishes a complete harmonic progression and signals the end of a musical phrase or section. The dominant chord's tension is effectively released when it moves to the tonic, making it one of the most common and recognizable cadences used in various musical styles.

The other choices relate to different harmonic functions. The subdominant-resolving-to-dominant context mentioned does not create the same sense of closure and is instead a part of other musical progressions. The leading tone moving to the tonic also contributes to smooth melodic resolution but does not serve the broader harmonic function that an authentic cadence provides. Sequential modulation refers to the process of changing key within a sequence, which is unrelated to the concept of cadences altogether. Hence, the defining feature of an authentic cadence is specifically the resolution from the dominant to the tonic.