If you look at the "Cadence" chapter of a few conventional harmony textbooks you will come across many terms such as the following: authentic cadence, plagal cadence, perfect cadence, imperfect cadence, full cadence, half cadence, interrupted cadence, deceptive cadence, etc..

The list of names is quite bewildering and, what's more, different writers have given contradictory definitions as to what some of these terms actually mean.

I shall attempt to clear up some of the muddle by using only those terms which are necessary to describe every type of cadence, and by using the most commonly known of these terms when there is a choice. I shall also describe the psychological effect of each of the cadential types.

It must be remembered that all of these different types of cadence have been defined in reference only to the conventional major and minor tonalities. Their relevance to the more unusual scales and cadential progressions that I describe on The Cadence Page will be discussed at the end.

The different types of conventional cadence can be covered with just the following terms:

Authentic cadence
Perfect
Imperfect
Plagal cadence
Half cadence
Deceptive and interrupted cadence

The authentic cadence is one whose penult is V and whose final is I or i. In the major and minor tonalities this is the strongest type of cadence and powerfully determines the key centre. How strongly the final is felt to be at rest, depends on whether or not the authentic cadence is perfect or imperfect.

The perfect cadence is always authentic - it uses a V - I or V - i progression, but both triads are in root position, and the tonic note of the scale is in the highest part.

This is the most decisive cadence and the I (i) chord is felt to be very conclusive. Its strongest version is in the extended cadence IV - I_c - V - I, which is commonly used as the final ending in long pieces of music.

The perfect cadence can be seen as analogous to a full-stop.

The imperfect cadence is also always authentic, but now the triads are not in root position, and/or the tonic is not in the highest part.

When the tonic note is not in the highest part, it slightly weakens the decisiveness of the conclusion.

When the V is inverted, it weakens the decisiveness and strength of the progression.

When the I (i) is inverted, it weakens the conclusiveness of the tonic to a much greater degree. Although the key centre is strongly established by this progression, it does not provide a proper sense of conclusion because the inversions of the triads are not, in themselves, stable entities. Such a cadence is often used where a perfect cadence would seem overly emphatic - it does not check the flow of the music too severely. This type of cadence is perhaps analogous to a comma.

One should not be too emphatic in deciding whether or not an authentic cadence is perfect or imperfect - its ultimate effect is also strongly influenced by its context and there is really a continuum between the two. I have simply defined the perfect cadence such that it only represents the most emphatic relationship between penult and antepenult.

The plagal cadence is usually defined as one whose penult is IV and whose final is I (or whose penult is iv and whose final is i).

Some theorists have widened its definition to include cadences whose penult is on the subdominant (flat) side of the tonic e.g. ii - I.

In my opinion, the term is best used to describe cadences in which the penult contains the tonic degree. The only triads which contain the tonic degree (except for I and i) are IV, iv, VI and vi. The vi triad is not found as the penult in any effective cadence and so it can be ignored.

This gives the following endings: IV - I, iv - i, iv - I, IV - i, VI - i.

All of these cadences have a penult which can also harmonise the tonic note. This is why the plagal cadence is sometimes called the "Amen cadence" because of its use at the end of hymns. They give a gentle ending and the penult gives the effect of being a delayed or decorated resolution to the final.

The plagal cadence is frequently used after a perfect cadence, because it is not as tonally decisive as the perfect cadence. In such a progression the perfect cadence has strongly asserted the tonicity of I (i), allowing the subsequent plagal cadence to decorate this bedrock.

It is hard to find a grammatical analogue for the plagal cadence, but perhaps it can be described as the words "The End" at the end of a film - we know the film has ended, we're just getting a little decoration and confirmation.

It can also be employed at the end of a phrase in the middle of a musical flow, in which case it is more akin to a comma.

The half cadence is the same as an authentic cadence except that it is not completed - the cadence proceeds as usual, but it stops on the V chord. The V is frequently preceded by I ⁶₄.

This cadence provides a sort of temporary pause, but it is not a completion, resolution or a point of rest. It does, however, strongly assert the tonality.

These two terms are generally considered to be synonymous, but I have chosen to make a distinction between them. I have done this to more clearly define two similar, but different, types of cadential progression.

These cadences are the same as the authentic, except that instead of resolving from V to I (i) they resolve to another chord. The effect of this progression is dependent on the chord to which they resolve.

Deceptive

When V resolves to vi it sounds like a very effective resolution because vi is able to function as a genuine tonic - i.e. as a chord of rest and resolution. In this way this cadence is genuinely deceptive - the ear is expecting something, but it is given something else which has such a similar function that it is not easily detected - the ear is fooled.

There are other chords which may be deemed to be deceptive finals - IV_b and I⁷ are good examples. The IV is usually used in its first inversion and sounds similar to vi. I⁷ sounds like I but it has a different function - as a dominant seventh it cannot function as an effective tonic (in common practice tonal harmony) and seeks resolution to a triad a fifth below. Due to their similarity to genuine tonics both these chords have been introduced deceptively. Any other chords which bear similarity to the genuine tonics of I, i and vi, can be introduced deceptively.

Interrupted

When the V chord resolves to a chord which bears no relation to a true tonic, the cadence can be described as interrupted. It sounds like a normal cadence, but it suddenly changes tack and instead of resolving it moves to a completely place. The cadence has been interrupted.

Please remember that there is no distinction made between the interrupted and deceptive cadences in conventional music theory, they are simply synonyms and either will be chosen at the behest of the author. The distinction is one that I have made for the purpose of extra clarity.

The cadential forms that I have described were invented to be used with the conventional major and minor scales. There is nothing, however, to stop their use in the more unusual scales described in the Scales Page.

We may summarise the forms above to be those which complete their resolution (full cadences), and those which stop on the penultimate chord (the half cadences); cadences which contain the tonic note in both the penult and final (plagal cadences), and finally all those cadences which resolve to a chord other than that expected (deceptive or interrupted cadences).

These four types of form, which are each felt to be of enough significance to deserve their own description, can be applied to any cadential chord progression from the eight tonal harmonic scales.