Magnitude Zero wrote:This was an awesome read, thank you.
Welcome!
Musical Form 101Prerequisites:- The ability to read music
- Understanding of the major, natural minor, and harmonic minor scales
- A general understanding of chords, including their inversions and notation
- Common practice voice leading
(If you don't know these already, there are links and tutorials that have been previously posted in this thread.

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1. Basic chord progressions and their functionsThe basic harmonic functionsCaplin divides the chords of the diatonic scale into three groups based on their function in tonality:
Tonic,
Pre-dominant, and
Dominant. You should probably already know that dominant harmony tends to
pull towards the tonic. Similarly, tonic harmony tends to pull towards pre-dominant, and pre-dominant, while it doesn't really pull towards dominant harmony, does serve to prepare the listener for it. Caplin includes two chords as pre-dominant: II and IV. He also includes two chords as tonic: I and VI (the latter particularly in first inversion), and two chords as dominant: V and VII. The fourth scale degree usually has a tendency towards the fifth scale degree (due to how we've been listening to music for hundreds of years), hence II and IV, which both include the fourth, lead towards dominant harmony. The V and VII chords both contain the prominent seventh scale degree, which leads to the tonic.
(Note: This means that when using the minor mode, the seventh must be raised as in the harmonic minor for the dominant function to exist.) From this, you can probably guess that I and VI are both included as tonic because they contain the tonic scale degree. Generally, the functional tones of a chord are the root and third, leaving the fifth as less important. Try it for yourself: Play a naked fifth--it sounds like a naked fifth, relatively hollow and empty. Play a third--it sounds richer, like it could be a chord.
Harmonic prolongationHarmonic prolongation is probably the most basic type of harmonic progression used throughout the common practice period. Harmony is said to be prolonged when the same harmony begins and ends a progression. Most commonly used are tonic and dominant prolongation, due to their importance.
(Note: The contrast between tonic and dominant is the driving force behind most western classical music.) To keep the prolongation perceptible to the listener, prolongational progressions are usually limited to three or four chords, and a couple rules are usually enforced. There are only a few types of progressions used for prolonging harmony.
Pedal point: The most basic way of prolonging harmony isn't actually a progression at all. The harmony is simply sustained, either as one really long chord (ex. 1), or the functional tone could be sustained while other chords are played around it (ex. 2). When this occurs, the progression could be analyzed as every chord including the sustained tone.
Ex. 1: Melody plays over a tonic pedal. Ignore the highlighting--that's just Finale being stupid.
Ex. 2a: Tonic pedal in the soprano voice with other chords underneath. Could be analyzed C C7/E D7 G11
Ex. 2b: Tonic pedal in bass voice with other chords above. Stronger prolongation.Neighbor chords: When the first and last chords are on the same root and in the same position. Examples: I-II-I, V-IV-V, I6-III-I6, V-VII-V, I-VII-VI-I, I-III-II-I, I-III-IV-I, etc.
Progressions to avoid: Tonic prolongation where the dominant is the second-to-last chord, because it forms a perfect authentic cadence.
Passing chords: When the first and last chords are in different position. Examples: I-II-I6, I64-II6-III-I, etc.
Progressions to avoid: A progression which begins and ends with a different root, but same harmonic function (e.g. V6-VI-VII) is not a harmonic prolongation--it is a sequence.
Substitute chords: Prolongations can be extended by adding the other chord of the same function in the middle. Example: I-III6-VI-IV-I6.
SequencePretty simple to understand. Just pick an interval and do a root progression based on it (e.g. descending third: I-VI-IV-II-VII-V-III-I). The main purpose of a sequential progression is to destabilize the prevailing harmony, often for the purpose of modulation to a new key (i.e. add variety). Therefore, the progression usually begins with a functional chord in one harmonic region and ends with a functional chord in the same or another harmonic region. The fundamental idea of a sequence is a consistent intervallic motion in one or more of the voices (usually soprano and bass). Therefore, while a consistent root progression is the simplest form of sequence, you can liven things up a bit with inversions, as long as your voices form a consistent pattern. In sequential progressions where the bass moves by a third, you can even fill in the leap with inverted passing chords; this will give the progression some harmonic functionality that may or may not be desirable (or, more likely, won't really matter).
(Note: Caplin's book goes into way more detail about sequential progressions than I can fit here.)CadenceAlso pretty simple to understand. Cadences act as a point of repose, and help solidify the sense of key. There are two types: Authentic cadences and Half cadences. In an authentic cadence, harmony goes from dominant to tonic, and in a half cadence, from tonic or pre-dominant to dominant. In a full authentic cadence, the harmony actually goes tonic, pre-dominant, dominant, tonic, but just as often the first or second one of those is left off. An authentic cadence will always use V-I as the last two chords, never VII or VI, and a half cadence will always use V as the last chord, never VII. An authentic cadence which ends in VI is called an "escaped cadence," and is one of the most over-used tricks in the book. It works really well for keeping things interesting by delaying the actual cadence, but use it sparingly. (You can also use a different chord at the end, but VI is the most common choice.)
Part 2: Basic formal functions, next post -- coming soon!