In the previous section on harmonic function, the strong progression of V - I was discussed. Listen again to the example, and notice how the phrase does not sound over until the final I chord is sounded.
The final V - I chord progression is what we call a cadence. A cadence is combination of a certain strong harmonic progressions with a resolution to a strong beat that ends a phrase. Cadences might be thought of as the punctuation marks in music - some cadences sound quite final (!) while others only pause a moment (,) and still others leave the listener waiting for more (?). Cadences are easy to hear, but are sometimes harder to recognize in printed music. It is important to listen to the musical examples, and recognizing these musical punctuations.
The strongest type of cadence is an authentic cadence. There are two types of authentic cadences: a perfect authentic cadence (PAC) and imperfect authentic cadence (IAC) . In order for an authentic cadence to be perfect all of the following must be true:
All of these strict requirements make this the strongest and most final sounding of all cadences. You may think of it as a final period at the end of a paragraph or an exclamation point (!). A PAC is usually found at the end of works and often at the end of significant sections.
In an imperfect authentic cadence, the only requirement is that the harmonic progression must be V - I or vii - I, or with added sevenths on the V or vii chords. The chords may be inverted, and the melody may end on a pitch other than tonic. Because of the more general nature of the IAC, it sounds less final, but still strong enough to be used at minor stopping points in a work when the composer wishes the music to cadence, but then go on. Musically, this cadence functions like a period at the end of a sentence.
When a V chord does not resolve up by fourth to a I chord, but instead resolves up by second to a vi, we call it a deceptive cadence (DC). Because a vi chord and a I chord have two notes in common. This cadence is not nearly as conclusive, or final, as an authentic cadence, and is never used to end a tonal work. However, it does provide a delightful "surprise" by resolving to a minor chord in major keys, and a major chord in minor keys. In a deceptive cadence, the vi chord is not used in first inversion. This is because of the similarity to the I chord - it will sound like a "wrong note I chord" rather than a vi chord.
The half cadence (ending on V)is perhaps most like a comma (,) because it cannot end a phrase. The unstableness of the dominant chord sets up the following phrase. In a half cadence (HC) the V chord may be preceded by any other chord. The chord that follows a half cadence may be any chord, however, I or vi are most common.
Another specific, but rarer, type of half cadence is a phrygian half cadence (iv6 - V) was popular during the Baroque period. Phrygian Half Cadences only occur in minor keys, and must consist of a first inversion iv chord that resolves to a root position V or V7 chord. It refers to a common type of cadence that was used in music written in the phrygian mode, but was later frequently used to end the slow middle movement of a concerto, when the composer wished for the final movement to begin without an extended break. The second movement of Bach's Brandenburg Concerto No. 2 is perhaps one of the shortest complete movements in the literature, and consists only of a phrygian cadence.
The Plagal cadence, IV - I is actually a regression, but through continual and prominent use by composers over the centuries, it has become a common, conclusive cadence. This is the "Amen" cadence used at the end of most church hymns.
As mentioned, cadences are usually quite easy to recognize when heard. In common practice music, cadences occur at regular intervals, usually every 4 or 8 measures, but in slower works may occur more frequently. Notice also that not every V - I, for example, is a cadence. A cadence is both harmonic and melodic -- occurring at important points in the music. Listen to the following example to hear how a variety of cadences are used to bring the music to a regular ebb and flow, and how the type of cadence can lead the listener to expect what is to follow.