Seeing the whole system as one connected machine.
What you’ll learn in this section
- How the five engines form a single connected system
- Cadences — how phrases end, and how they build into whole pieces
- The dependency ladder that ties every idea together
- How the advanced ideas reinforce the underlying system
- Cadence recognition and harmonisation in practice
The full picture
The five engines are not independent — they form a single coherent system.
How everything connects
The tone-semitone pattern gives you a scale. A scale immediately yields the tonic (first note), the dominant (fifth note), and the relative minor (sixth note). The interval stack then tells you what kind of chord can be built on each of those notes by applying the stacking rule to the notes available within the scale.
Key signatures, scale types, chord types, and the relationships between chords all follow from the pattern. Once the pattern is understood, the rest is largely derivation.
What this gives your playing
Know why a key signature exists — it is just the tone-semitone pattern written once at the start — and you stop making random accidental slips, because every note now feels like it belongs. A player who understands chord structure hears chord progressions in their music rather than a sequence of unrelated note clusters. A player who understands the relative relationship recognises when a piece shifts key and adjusts naturally.
Understanding the engines gets you to Grade 4 comprehension. Grade 4 playing also requires time at the piano. The two support each other — but neither substitutes for the other.
The dominant asks a question
A cadence is how a phrase ends — and most endings hinge on chord V, which leans hard toward home. The same approach can land four different ways. Press each ending and watch the ball: where it comes to rest is the cadence.
This is why a song sounds finished. That V→I landing closes almost every hymn, anthem and pop chorus you know — the musical full stop.
Train your ear
Finished or left hanging? Play the two chords, then judge the ending.
Try it: the four cadences
From cadences to whole pieces
Everything so far — scales, chords, cadences — exists to serve the level you actually listen at: the whole piece. The bridge between a chord progression and a finished piece is the phrase.
A phrase is a musical sentence: a short stretch of melody that ends with a cadence, the way a sentence ends with punctuation.
An imperfect cadence (ending on V) is like a comma — it leaves you expecting more.
A perfect cadence (V–I) is like a full stop — it sounds finished.
Composers pair these constantly: a phrase that ends “open”, then an answering phrase that ends “closed.” That question-and-answer shape is the most common unit in all tonal music.
Stack phrases up and you get form — the architecture of the whole piece. The simplest is binary form (an A section, then a contrasting B section). Add a return and you have ternary form (A–B–A): a home idea, a departure, and a homecoming. Even large works are mostly this same instinct scaled up — statement, journey away, return — the very same home/away/return that drives a single I–IV–V–I, now operating across an entire piece.
That is the point of the whole course in one sentence: the small patterns and the large shape are the same idea at different scales. Hear the pull from V back to I in a single cadence, and you are hearing, in miniature, what makes a whole piece feel like a journey home.
The whole thing on one ladder
Every idea in this course sits in a single dependency chain. Each layer is built from the one above it — which is why understanding the early ones makes the later ones feel almost inevitable rather than arbitrary.
Read it downward: the keyboard gives you notes; the gaps between notes are intervals; a particular pattern of intervals is the major scale; numbering that scale gives degrees; a scale treated as home is a key; stacking degrees gives triads; the relationships between those chords are harmonic function; functions punctuate as cadences; and cadences shape the phrases that make up whole pieces. Master the top of the ladder and the rest is detail.
Build progressions from Roman numerals and hear how function drives the music — I, IV, V and the chords around them.
Every chord in a key is built from notes of that scale. Chord I uses notes 1, 3, 5. Chord ii uses 2, 4, 6. The scale and its chords share the same pool of notes.
Recognising cadences in music
Identifying a cadence in a piece means looking at the last two chords of a phrase and asking: where does it land, and does it sound finished?
- Perfect cadence (V→I): sounds conclusive. The dominant chord (built on degree 5) resolves to the tonic. Most common at the end of a piece or section.
- Imperfect cadence (?→V): sounds unfinished, like a question. Any chord moving to V. Common at the mid-point of a phrase.
- Plagal cadence (IV→I): sounds settled but softer than perfect. The “Amen” cadence in hymns.
- Interrupted cadence (V→VI): sounds surprising. The ear expects V to go to I; instead it goes to VI (the relative minor in major keys). Used for dramatic effect mid-phrase.
Find the phrase endings first (usually every 2 or 4 bars). Look at the bass note of the last two chords of each phrase. If the bass falls by a fifth (e.g. G down to C in C major), that is a perfect cadence. If the bass rises by a fourth to the dominant, that is likely an imperfect cadence or a perfect one. Use the bass as your guide — it carries the harmonic movement most clearly.
✔ Quick check: A phrase ends on the dominant chord (V). What type of cadence is this?
✔ Quick check: A phrase ends with the chord sequence V→I. What cadence is this, and how does it sound?
✔ Quick check: The chord sequence IV→I at the end of a phrase. Which cadence type?
✔ Quick check: The ear expects V to resolve to I, but instead the music moves to chord VI. What is this called?
Cadences happen at phrase ends — look for two chords before a pause or a long note. Check whether the last chord is I (perfect/plagal/interrupted) or V (imperfect).
How the engines connect in Essentials — the five engines as one system: scale → tonic/dominant/relative-minor → chords → cadences. Revisit →
The engines working together
Cadences
A "cadence" is a pair of chords at the end of a musical phrase that creates a sense of arrival or pause. The four main cadences all involve the relationship between tonic and dominant chords that the pattern generates.
Perfect cadence (V–I): dominant to tonic. Sounds finished and resolved. The most conclusive ending.
Imperfect cadence (I–V or IV–V): ends on the dominant. Sounds like a question or a pause mid-thought.
Plagal cadence (IV–I): subdominant (fourth note) to tonic. Sounds gentle, hymn-like. Often called the "Amen" cadence.
Interrupted cadence (V–VI): dominant resolves unexpectedly to the sixth degree rather than the tonic. The surprise creates forward momentum rather than closure.
Putting it to work in your playing
Every cadence, chord progression, and key change in the music you are learning involves these five engines. The tone-semitone pattern tells you which notes belong; the interval stack tells you how chords are built; the relative relationship explains modulations to nearby keys; time signatures organise the pulse; and the stave encodes everything visually. Understanding these connections means each new piece reveals its own logic rather than presenting a set of arbitrary choices to be memorised.
From cadences to whole pieces
Everything so far — scales, chords, cadences — exists to serve the level you actually listen at: the whole piece. The bridge between a chord progression and a finished piece is the phrase.
A phrase is a musical sentence: a short stretch of melody that ends with a cadence, the way a sentence ends with punctuation.
An imperfect cadence (ending on V) is like a comma — it leaves you expecting more.
A perfect cadence (V–I) is like a full stop — it sounds finished.
Composers pair these constantly: a phrase that ends “open”, then an answering phrase that ends “closed.” That question-and-answer shape is the most common unit in all tonal music.
Stack phrases up and you get form — the architecture of the whole piece. The simplest is binary form (an A section, then a contrasting B section). Add a return and you have ternary form (A–B–A): a home idea, a departure, and a homecoming. Even large works are mostly this same instinct scaled up — statement, journey away, return — the very same home/away/return that drives a single I–IV–V–I, now operating across an entire piece.
That is the point of the whole course in one sentence: the small patterns and the large shape are the same idea at different scales. Hear the pull from V back to I in a single cadence, and you are hearing, in miniature, what makes a whole piece feel like a journey home.
The whole thing on one ladder
Every idea in this course sits in a single dependency chain. Each layer is built from the one above it — which is why understanding the early ones makes the later ones feel almost inevitable rather than arbitrary.
Read it downward: the keyboard gives you notes; the gaps between notes are intervals; a particular pattern of intervals is the major scale; numbering that scale gives degrees; a scale treated as home is a key; stacking degrees gives triads; the relationships between those chords are harmonic function; functions punctuate as cadences; and cadences shape the phrases that make up whole pieces. Master the top of the ladder and the rest is detail.
To harmonise a melody note: check which chords of the key contain that pitch. Pick the chord whose harmonic function fits the phrase position (stable inside, tension at the end).
Choosing chords to harmonise a melody
Knowing I, II, IV and V is one thing. Applying them to harmonise a melody is the practical skill. The process is systematic:
- Identify the key. Look at the key signature and the opening and closing notes.
- Find the cadence points. The last bar is almost always a perfect cadence (V–I). The half-way point is often an imperfect cadence (ending on V).
- Choose a chord for each marked beat. The chord must contain the melody note. Work out which chords of the key include that note: in C major, the note E appears in I (C-E-G), II (D-F-A)? No — II is D-F-A. E is in I and VI. Use I or VI.
- Prefer chords that move by fourth or fifth. I→IV, I→V, IV→I, V→I all sound strong. Avoid repeating the same chord in two adjacent beats unless you intend it.
- Check every melody note fits its chord. A melody note does not have to be the root — it can be the third or fifth of the chord — but it must be one of the three chord tones.
Melody opens on G (beat 1), moves to A (beat 2), then E (beat 3), then C (beat 4). Beat 1: G is in I (C-E-G) or V (G-B-D). Beat 4: C is in I or IV. If beat 4 is I and beat 3 should lead to it, use V on beat 3 (E is in I too, but V→I is the strongest move). So: I, ?, V, I — fill beat 2 (A): A is in II (D-F-A) or VI. II fits well. Result: I–II–V–I.
Recognising cadences in music
Identifying a cadence in a piece means looking at the last two chords of a phrase and asking: where does it land, and does it sound finished?
- Perfect cadence (V→I): sounds conclusive. The dominant chord (built on degree 5) resolves to the tonic. Most common at the end of a piece or section.
- Imperfect cadence (?→V): sounds unfinished, like a question. Any chord moving to V. Common at the mid-point of a phrase.
- Plagal cadence (IV→I): sounds settled but softer than perfect. The “Amen” cadence in hymns.
- Interrupted cadence (V→VI): sounds surprising. The ear expects V to go to I; instead it goes to VI (the relative minor in major keys). Used for dramatic effect mid-phrase.
Find the phrase endings first (usually every 2 or 4 bars). Look at the bass note of the last two chords of each phrase. If the bass falls by a fifth (e.g. G down to C in C major), that is a perfect cadence. If the bass rises by a fourth to the dominant, that is likely an imperfect cadence or a perfect one. Use the bass as your guide — it carries the harmonic movement most clearly.