Music Theory Resources
Cadences are patterns of two chords that occur at the end of phrases, sections, or movements. A cadence indicates some kind of closure, or ending. This closure may be temporary, such as internal cadences, or final, as in final cadences (the ending of a piece). The following list of cadences proceeds from the most closed to the most open. They may occur in either major or minor modes.
Cadences are musical formulas that function like punctuation marks in a sentence. These formulas are conventions that have developed over time to signal the end of a musical unit such as a phrase. Cadences involve the interaction of melody, harmony, rhythm, and meter, and usually mark the end of a phrase. Some cadences sound conclusive, complete, and resolved (like a period), while others sound incomplete (like a comma or colon). The most complete type of cadence is the authentic cadence, which moves from V to I. In a half cadence the progression is stopped on V, which makes it feel unfinished.
Sometimes composers will even start a cadential formula, but instead of arriving at the cadence as expected, they will interrupt or change the formula with a deceptive cadence.
Perfect Authentic Cadence
Perfect authentic cadence (PAC): a dominant-to-tonic cadence: V-I, V7-I, V-i, V7-i: the penultimate chord is V in root position; the final chord is I (i) in root position but also with the root in the soprano. The dominant chord can be a triad, a dominant-seventh chord, or a Vsub6. This is the most final, most closed type of cadence. The top voice (soprano, melody) is either 2-1 or 7-1 (with the use of the Vsub6, it would be 3-1). The bass voice is always 5-1.
Imperfect Authentic Cadence
Imperfect authentic cadence (IAC): also a dominant-to-tonic cadence, but the dominant chord can be any form of dominant chord other than a root position V chord, and the tonic chord can be any version of the tonic triad. In other words, it can be any dominant-to-tonic cadence that is not a PAC. This cadence is less closed than the PAC. Examples would include: V6-I, vii-I. The most common version is similar to a PAC, with both the V and I chords in root position, but the I chord has either the third or fifth of the triad in the soprano.
Plagal cadence (PC): IV-I (iv-i, iv-I). Both triads are in root position. This is the "Amen" cadence. It often occurs after a final PAC.
Deceptive cadence (PC): The dominant triad (or dominant-seventh chord) resolves not to I, but to vi (or VI or bVI) as a tonic substitute. Major Minor V-vi V-VI V-bVI (borrowed)
Half cadence (HC): A cadence that ends on the dominant triad (or possibly the dominant-seventh chord). It often is preceded by I: I-V, or I6/4-V. This type of cadence can be found at the end of the antecedent phrase in a period structure, or at the end of a phrase that prepares for the return of tonic or the main theme.
Phrygian Half Cadence
A Phrygian half cadence (PHC) is a special type of half cadence in which the dominant triad in root position is preceded by the iv6 (and only this chord!). It gets its name from the half-step motion in the bass. It may be used in either major or minor mode.