First of all, what is cadence? Cadence is simply known as point of rest. It is a musical punctuation. A melody without cadence(s) is meaningless. Cadence is a two-chord affair. A harmonic cadence usually consists of just two chords. It’s a progression of at least two chords. It is usually found or heard at the end of a piece of music, or sections and musical phrases within it. Differently put, it signals the end of a phrase, section or the entire composition.
There are many types of cadences. Here, only five are highlighted. These five are known as the conventional or traditional cadences. Please note that: “I” means the tonic triad (also known as chord one). “V” means the dominant triad (chord five). Here, Roman numerals are used in outlining the chords. The use of capital letter(s) is to indicate that the chord is major while small letter(s) indicate that the chord is minor. Types of progression (such as circle progression, ascending 5ths and descending 4th, ascending 2nds, descending 3rds) is not the topic of discussion here; we have to leave it for another time.
Perfect Authentic Cadence (PAC). A cadence is said to be perfect authentic when there’s a V-I (chord five to one) progression. It can also be called dominant –tonic cadence (V-I in major keys, V –i in minor keys). The two chords must not be inverted, and the outer voices (soprano and bass) must take the root of the tonic triad (I). That is, the root of the tonic triad must be the highest and lowest sounding pitches. It suggests conclusion or finality. It’s a very strong cadence. Examples are illustrated below.
Imperfect Authentic Cadence (IAC). This is still a V-I progression but differs if at least, one of the two chords is inverted (E.g. V6 to I, or V to i6). In other words, it is differentiated from PAC if one of the outer voices doesn’t take the root of the tonic triad (I). It can also differ if the highest sounding pitch in the tonic triad is either the 3rd or the 5th factor instead of the root. Sometimes, it can differ if the dominant triad (V) is replaced with vii0, making it vii0 to I or i. It’s weaker than PAC. Examples are illustrated below.
Half Cadence (HC). This is a situation whereby any of the chords moves to V. It gives room for a large number of possibilities. It could be IV- V, vi-V, ii-V, and I-V. It doesn’t in any way suggest finality or conclusion. Examples are illustrated below.
Deceptive Cadence (DC). This can also be called interrupted cadence (IC). Here, the first chord V, and the second is not I. It could be V-vi, V-IV6 in a major key, V –VI in a minor key. It doesn’t suggest finality. If you are in a major key, III-vi could be interpreted as a deceptive cadence. But in a minor key, III-vi (which is actually V-i) could either be a PAC or IAC, depending on the voicing. Examples are illustrated below.
Plagal Cadence (PC). This is fondly called “Amen” cadence. It’s a IV-I progression (IV-I in major keys, iv to i in minor keys). It’s commonly used for ending hymns. It’s used in singing the “amen” section of hymns. Sometimes, ii6 to I is interpreted as plagal. Examples are illustrated below.
Extra: There are many other kinds of cadences which are simply variations of the traditional cadences. These include mixolydian cadence (v-I), Phygian half cadence (iv-V), Third relationship cadence, which results from a harmonic progression in which the roots lie a 3rd apart (iii6 to I). Examples are illustrated below.