Harmony in depth: diatonic chords and Roman numeral or chord-symbol labelling, common progressions, cadences (perfect, plagal, imperfect, interrupted), consonance and dissonance, and modulation

What this dot point is asking

Harmony lives inside the concept of pitch and is where the most technical theory in HSC Music sits. It is how chords are built, chosen and connected to create tension and resolution. This dot point asks you to label chords by Roman numeral and chord symbol, recognise the common progressions of tonal and popular music, identify the four cadences by ear, distinguish consonance from dissonance, and explain modulation, so that you can both hear harmony in the aural exam and analyse it in scores for musicology.

The answer

Diatonic chords and how to label them

A diatonic chord is a triad built on each degree of a scale using only the notes of that key. In a major key the chords are I and IV and V major, ii and iii and vi minor, and vii diminished. Two labelling systems run in parallel. Roman numerals describe a chord by its scale degree, so in C major chord I is C, IV is F and V is G; upper case marks major, lower case minor. Chord symbols name the chord directly (C, F, G, Am, Dm7, G7), the system used in lead sheets and popular music. You should be fluent in both, since Music 2 score analysis tends to use Roman numerals while popular-music charts use symbols.

Seventh chords and extensions

Adding a third above the triad gives a seventh chord. The dominant seventh (V7) is especially important because its built-in dissonance pulls strongly toward the tonic, driving most cadences. Major seventh, minor seventh and diminished seventh chords add colour, and extended chords (ninths, elevenths, thirteenths) are common in jazz. Naming the chord quality (major, minor, dominant seventh) is as important as naming its root.

Common progressions

Tonal and popular music recycle a small set of progressions. The I-IV-V-I progression is the backbone of tonal harmony. The I-V-vi-IV progression underpins countless pop songs. The ii-V-I progression is the foundation of jazz harmony. The twelve-bar blues cycles I, IV and V across twelve bars. Recognising a progression by ear, even just hearing the bass move from tonic to dominant and back, gives you a strong harmonic observation quickly.

Cadences

A cadence is a harmonic punctuation point that closes a phrase. The perfect (authentic) cadence, V to I, sounds finished, like a full stop. The plagal cadence, IV to I, is the gentle "Amen" close. The imperfect (half) cadence ends on V, sounding unfinished, like a comma that needs continuation. The interrupted (deceptive) cadence moves V to vi, surprising the ear by avoiding the expected tonic. Identifying cadences is a frequent aural task because they reveal both harmony and structure, marking the ends of phrases and sections.

Consonance, dissonance and modulation

Consonance is a stable, restful sound; dissonance is tense and seeks resolution. Composers use the tension of dissonance and its release into consonance to create momentum, suspensions and expressive colour. Modulation is a change of key during a piece, often from the tonic to the dominant or relative minor, used to create contrast and structural movement. A clear sense of arriving in a new key, with new sharps or flats and a fresh tonal centre, is the signal of modulation.

Hearing and analysing harmony

To hear harmony, follow the bass line and listen for moments of tension and rest. Ask whether the harmony is major or minor, whether it sits still or moves, and where it resolves. In score analysis, label each chord with a Roman numeral or symbol, identify the cadences at phrase ends, and note any modulation or chromatic chords. Then connect the harmony to the structure and expression, since harmonic arrival often coincides with structural and dynamic arrival.

Writing about harmony

Be specific about chords and resolutions. Instead of "the harmony sounds tense then resolves", write "a dominant seventh creates tension that resolves to the tonic in a perfect cadence, closing the phrase". Tie harmonic events to the structure where you can.