Cadence Types

A cadence names the last two chords of a phrase, and the label depends on which chords they are and how they're arranged. V to I or vii to I resolves the leading tone and the active bass motion, so it sounds final: that's authentic. V to vi keeps the dominant's pull but lands on the wrong chord, a relative minor substitute, so the ear expects tonic and gets something else: deceptive. V staying put as the last chord, with nothing resolving, is a half cadence, a comma, not a stop. IV to I skips the dominant's leading tone entirely, giving a softer, hymn-like close: plagal.

Authentic cadences split further based on three strict conditions. A perfect authentic cadence needs both chords in root position, the progression must be V or vii to I (not i, and not IV), and the soprano must end on scale degree 1, the tonic pitch itself. Miss any one of those three and it drops to imperfect authentic: same V-to-I skeleton, but the soprano lands on the third or fifth of the tonic chord instead, or one chord is inverted. That's why reaching a tonic chord is never automatically authentic; the route matters as much as the destination.

Cadence type is how phrases get their shape, which connects directly to the Roman numeral analysis and voice-leading rules used throughout harmony: parallel fifths and octaves are forbidden partly because they'd blur the independent lines that make a cadence's resolution audible. Recognizing cadences also sets up phrase-level analysis, since a half cadence invites a second phrase to answer it, while a perfect authentic cadence closes the thought.