It might sound complicated, but all it means is that your tonic note is a focal point to the music. Usually, it's also the end "goal" for the melody. All the other pitches function in relation to that tonic pitch. For example, B-flat major and B-flat minor both share B-flat as the tonic pitch, but the other pitches in relation to the tonic are different (major vs. minor scale).

The concept of tonality has been present in Western music for several centuries, and has undergone a number of significant changes and developments over time.

The earliest forms of tonal music can be traced back to the music of ancient Greece, which was based on modes rather than keys. The medieval period saw the development of the system of church modes, which served as the basis for tonal music in the Western world for many centuries.

During the Renaissance, composers began to experiment with more chromaticism and dissonance in their music, and the system of church modes was gradually replaced by the system of major and minor keys that is still in use today. Tonality got really popular in music right around 1650. The Baroque period, which spanned the 17th and early 18th centuries, saw the development of tonal counterpoint and the creation of complex tonal structures.

In the Classical period, which followed the Baroque period, composers such as Haydn, Mozart, and Beethoven wrote music that was more transparent in its structure and more closely followed the rules of tonality. The Romantic period, which spanned the 19th century, saw a loosening of tonal structures and the use of more chromaticism and dissonance.

Western classical music veered away from tonality for a while around 1900, but tonal organization is still central to other genres such as folk and jazz.

Harmonic Progressions

Remember when we learned that each diatonic pitch and chord has a name? These diatonic chords usually occur in a predictable sequence called a harmonic progression that provides structure to the music. The way in which the chords are arranged in a harmonic progression can have a significant impact on the overall feel and mood of a piece of music.

Harmonic progressions can be described in writing using Roman numerals with appropriate markings for inversions as previously explained in this unit 3 study guide. The pace at which these harmonies change is called harmonic rhythm. Sometimes, the harmonic rhythm will change in the middle of a piece. You’ll notice that this changes the overall feel of the music quite a bit. Even if the tempo isn’t going faster, if the harmonies are changing faster, the piece feels faster.

Harmonic progressions give music a sense of direction and help it arrive at a harmonic goal. In tonal music, this goal is the tonic, which is built on the first degree of the scale for the key. For example, in the key of E major, the tonic would be an E major chord. The tonic chord is labeled with the Roman numeral I.

Dominant and Predominant Functionality

All other diatonic chords play a role in helping music arrive at the tonic. There are two main functions that these chords can have: dominant and predominant.

Chords that have a dominant function usually immediately precede the tonic, and movement from a dominant chord to a tonic chord often creates a feeling of resolution. There are two chords that typically have a dominant function: the V and the vii.

(Note: even in a minor key, dominant chords will only be V and vii, not v or VII.)

Why do these two chords lead to the tonic with such a sense of finality? Consider the pitches that make up each chord. We are in the key of Bb Major:

The V chord has scale degrees 5, 7, and 2, and the vii chord has scale degrees 7, 2, and 4. Scale degrees 7 and 2 can both resolve to the strong tonic note (scale degree 1) by a step, so we call them tendency tones. Scale degree 7 is a leading tone, so that tendency is even stronger.

The V chord is a stronger dominant than the vii chord because of a physics phenomenon called overtones. You won't need to know this for the AP exam, but you will need to know that scale degree 5 wants to resolve to scale degree 1, which also makes the V chord want to resolve to the I chord.

The V chord also resolves to the I chord especially well because it shares a pitch. The root of a V chord is the fifth of a I chord, so the voice leading from V to I is often very smooth and aesthetically appealing.

Predominant chords usually appear—you guessed it—before dominant chords. Lots of different chords can serve a predominant function in different cases, and they're a bit more complicated than dominant chords. We'll learn more about these in Unit 5. For now, though, it's useful to know that IV and ii chords often act as predominant chords.

The most basic harmonic progression in the CPP is tonic-dominant-tonic. Usually, this looks like I-V-I or i-V-i (depending on whether you're in a major or minor key).

Take the Happy Birthday song, for instance. The harmonic progression over each phrase is I-V-V-I-IV-V-I. Since some of these are repeated, you could also simplify it to I-V-I-IV-V-I. In one case, the predominant briefly sets up the dominant, but the song mostly alternates between I and V.

This is super common across tonal music, and you'll find it in everything from Bach to Taylor Swift.

In Western music, you'll find tonal music with lots of different harmonic progressions, but most will be some variation of tonic-predominant-dominant-tonic. Movement in the opposite direction (for example, tonic to dominant or dominant to predominant) is called a retrogression.

At the end of a musical phrase, the harmonic progression is called a cadence. There are four main types of cadences: half cadence; deceptive; plagal; and authentic.

Cadences

A half cadence occurs when a musical phrase ends on a V chord. Because the V chord has a dominant function, the half cadence usually feels unresolved or unfinished. Phrases that end in a half cadence sound a bit like a question, which is then answered by another phrase that ends with a stronger cadence.

A deceptive cadence has a V chord that sounds like it should resolve nicely to a I/i chord, but instead progresses to a different chord. In many cases, deceptive cadences move to a vi/VI chord or a IV/iv chord, but any non-tonic chord can end a deceptive cadence.

A plagal cadence (sometimes also called an "amen" cadence, since it is common in hymns) moves from the IV/iv chord to the tonic I chord. Although there is no dominant chord, plagal cadences are usually considered pretty strong resolutions.

The authentic cadence comes in two forms: the perfect authentic cadence (PAC) and the imperfect authentic cadence (IAC). Both involve the dominant V chord (or dominant-functioning chord, such as a vii chord) resolving to the tonic I chord, but the PAC is stronger because both chords are in root position (where they are more stable), and the soprano voice ends on scale degree 1. If either the V chord or the I chord are inverted or if the soprano ends on a non-tonic pitch, then the cadence is an IAC.

Here is the Imperfect Authentic Cadence (IAC):

Here is a Perfect Authentic Cadence (PAC):

You can categorize these cadences as either conclusive or inconclusive based on their strength and finality. Inconclusive cadences are usually followed by more music, while conclusive cadences are often reserved for the end of a piece, movement, or other large music structure. Half, deceptive, and inauthentic perfect cadences are inconclusive, while plagal and perfect authentic cadences are conclusive.

Some cadences are so iconic that they have their own special name. The most common of these is the Picardy third, which is a V-I cadence (observe the major quality of the tonic chord) in a musical work that is in a minor key.

Image via Wikimedia Commons

🦜 Polly wants a progress tracker: In Roman numerals, what are the four possible harmonic progressions that follow the tonic-dominant-tonic convention? (Hint: don't forget both major and minor!)

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