Music Theory: Chords, Keys, Major and Minor
Music theory is the study of how music works: how notes, rhythms, scales, keys and chords fit together, and the words and symbols used to write them down. A chord is three or more notes played together; the commonest is a triad of a root, a third and a fifth, such as C E G (C major). Classfern’s free theory hub explains each topic and lets you hear it.
Works in the UK and the US. This version uses UK music words (bar, crotchet, stave) and UK year groups; the US version uses measure, quarter note, staff and US grades. · US version of this page
Key facts
- An octave has 12 semitones; a tone is 2 semitones.
- A major triad is root + major 3rd (4 semitones) + perfect 5th (7 semitones); a minor triad has a minor 3rd (3 semitones) instead.
- There are 12 major and 12 minor keys to play in; key signatures run from 0 to 7 sharps or flats (15 major key signatures, counting the three enharmonic pairs).
- A sharp (♯) raises a note by one semitone, a flat (♭) lowers it by one, and a natural (♮) cancels either.
- Four main cadences: perfect (V–I), plagal (IV–I), imperfect (ending on V) and interrupted (V–vi).
- UK theory exams have 8 grades; the Classfern levels below cover the ground of Grades 1–5.
What is music theory?
Music theory is the study of how music is built and written down. It covers rhythm and time, pitch and the stave, scales and keys, intervals, chords and harmony, and form – the words and symbols musicians use to read, write and talk about music.
You can think of it as the grammar of music. A music theory class in school usually starts with reading notes and rhythms, then moves to scales, key signatures, intervals and chords, and later to harmony, cadences and writing your own music. Learning it helps you read faster, learn pieces more quickly, play by ear and compose.
Hear it: chords, scales and cadences
Press any ▶ button to hear the example. The sound is made by Classfern’s piano in your browser, and the player only loads when you press a button.
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What are chords in music?
A chord is three or more different notes sounded together. The basic chord is a triad: a root note, the note a third above it and the note a fifth above it. C major is C, E and G; C minor is C, E flat and G. Chords are named after their root and their quality: major, minor, diminished or augmented.
Chords are often written as chord symbols above the music: C means C major, Cm (or C min) means C minor, C7 adds a minor 7th (B♭), and Cmaj7 adds a major 7th (B). The table below spells every major and minor triad; press a button to hear it.
| Major triad | Minor triad |
|---|---|
| C: C E G | Cm: C E♭ G |
| D♭: D♭ F A♭ | C♯m: C♯ E G♯ |
| D: D F♯ A | Dm: D F A |
| E♭: E♭ G B♭ | E♭m: E♭ G♭ B♭ |
| E: E G♯ B | Em: E G B |
| F: F A C | Fm: F A♭ C |
| F♯: F♯ A♯ C♯ | F♯m: F♯ A C♯ |
| G: G B D | Gm: G B♭ D |
| A♭: A♭ C E♭ | G♯m: G♯ B D♯ |
| A: A C♯ E | Am: A C E |
| B♭: B♭ D F | B♭m: B♭ D♭ F |
| B: B D♯ F♯ | Bm: B D F♯ |
What is the difference between major and minor?
Major and minor differ by one note: the third. A major chord or scale has a major third (4 semitones above the root), and a minor one has a minor third (3 semitones). Most listeners hear major as brighter or happier and minor as darker or sadder, though music can be happy in a minor key too.
Every major key has a relative minor that shares its key signature, three semitones lower: C major and A minor have no sharps or flats; G major and E minor both have one sharp (F♯). A parallel minor starts on the same note: C major and C minor.
The minor scale comes in three forms. The natural minor uses the key signature as it is (A B C D E F G A). The harmonic minor raises the 7th note (G♯ in A minor). The melodic minor raises the 6th and 7th going up (F♯ and G♯) and uses the natural minor coming down.
What are sharps and flats?
A sharp (♯) raises a note by one semitone and a flat (♭) lowers it by one semitone. On a piano, C sharp is the black key just right of C, and E flat is the black key just left of E. A natural sign (♮) cancels a sharp or flat. The same key can have two names, such as C♯ and D♭.
Notes with two names are called enharmonic. In written music, sharps or flats can appear as a key signature at the start of every line (they apply all the way through) or as accidentals beside a single note (they last until the end of the bar). A double sharp (𝄪) raises a note by a tone and a double flat (𝄫) lowers it by a tone.
| Signature | Major key | Relative minor | Sharps or flats |
|---|---|---|---|
| 0 | C major | A minor | – |
| 1♯ | G major | E minor | F♯ |
| 2♯ | D major | B minor | F♯ C♯ |
| 3♯ | A major | F♯ minor | F♯ C♯ G♯ |
| 4♯ | E major | C♯ minor | F♯ C♯ G♯ D♯ |
| 5♯ | B major | G♯ minor | F♯ C♯ G♯ D♯ A♯ |
| 6♯ | F♯ major | D♯ minor | F♯ C♯ G♯ D♯ A♯ E♯ |
| 7♯ | C♯ major | A♯ minor | F♯ C♯ G♯ D♯ A♯ E♯ B♯ |
| 1♭ | F major | D minor | B♭ |
| 2♭ | B♭ major | G minor | B♭ E♭ |
| 3♭ | E♭ major | C minor | B♭ E♭ A♭ |
| 4♭ | A♭ major | F minor | B♭ E♭ A♭ D♭ |
| 5♭ | D♭ major | B♭ minor | B♭ E♭ A♭ D♭ G♭ |
| 6♭ | G♭ major | E♭ minor | B♭ E♭ A♭ D♭ G♭ C♭ |
| 7♭ | C♭ major | A♭ minor | B♭ E♭ A♭ D♭ G♭ C♭ F♭ |
Two quick tricks: in a sharp key, the major key is one letter name above the last sharp (last sharp F♯ → G major). In a flat key, the second-to-last flat names the key (B♭ E♭ → B♭ major); one flat is F major.
What is a key and a tonic in music theory?
A key is the home scale a piece is built on, and the tonic is its home note – the first note of that scale, where the music feels at rest. A piece in G major uses the G major scale, usually ends on G, and has a key signature of one sharp.
The notes of a scale are numbered from the tonic as scale degrees: 1 tonic, 2 supertonic, 3 mediant, 4 subdominant, 5 dominant, 6 submediant, 7 leading note (in minor keys, the subtonic when it is not raised). Chords built on them are written in Roman numerals: I, ii, iii, IV, V, vi and vii° in a major key.
What are intervals, semitones and tones?
An interval is the distance between two notes. The smallest step in Western music is the semitone, the distance between two neighbouring keys on a piano; two semitones make a tone. An interval is named by counting letter names (C to E is a 3rd) and by its quality (major, minor or perfect).
| Interval | Semitones | Example |
|---|---|---|
| Minor 2nd | 1 | C to D♭ |
| Major 2nd | 2 | C to D |
| Minor 3rd | 3 | C to E♭ |
| Major 3rd | 4 | C to E |
| Perfect 4th | 5 | C to F |
| Tritone (augmented 4th) | 6 | C to F♯ |
| Perfect 5th | 7 | C to G |
| Minor 6th | 8 | C to A♭ |
| Major 6th | 9 | C to A |
| Minor 7th | 10 | C to B♭ |
| Major 7th | 11 | C to B |
| Octave | 12 | C to C |
The tritone (6 semitones, such as C to F♯) splits the octave exactly in half and sounds tense. Its name means “three tones”.
What is a cadence in music theory?
A cadence is the pair of chords at the end of a phrase that makes it sound finished or unfinished, like punctuation in a sentence. The four main cadences are perfect (V–I), plagal (IV–I), imperfect (ending on V) and interrupted (V–vi).
| Cadence | Chords | How it sounds | Hear |
|---|---|---|---|
| Perfect cadence (US: authentic) | V – I | Finished, like a full stop | |
| Plagal cadence | IV – I | Finished but gentle (the “Amen” at the end of many hymns) | |
| Imperfect cadence (US: half) | any chord – V | Unfinished, like a question or a comma | |
| Interrupted cadence (US: deceptive) | V – vi | A surprise: the ear expects I but hears vi |
To identify a cadence, find the last two chords of the phrase and name them in Roman numerals. If the second chord is I, it is perfect (from V) or plagal (from IV); if it is V, it is an imperfect cadence; if V goes to vi, it is interrupted.
Note values and time signatures
Rhythm is the other half of theory. The UK names are used on this page; the US names are in the second column.
| Note | US name | Beats in 4/4 |
|---|---|---|
| Semibreve | whole note | 4 |
| Minim | half note | 2 |
| Crotchet | quarter note | 1 |
| Quaver | eighth note | ½ |
| Semiquaver | sixteenth note | ¼ |
A time signature such as 3/4 says how many beats are in each bar (top number) and which note gets one beat (bottom number). Cut time, 2/2 (also called alla breve), has two minim beats in each bar. A anacrusis (upbeat) is a note or two before the first full bar.
Music theory for beginners: what to learn, in order
Classfern’s free theory and aural tests are set out in five levels, like Grades 1–5 (Classfern’s own levels, not an exam board’s syllabus). Each topic below has a free lesson in Learn to Read Music.
| Level | What you learn | Start with |
|---|---|---|
| Level 1 (like Grade 1) | Treble and bass clef notes with one ledger line; semibreve to quaver and their rests; 2/4, 3/4 and 4/4; C, G, D and F major; intervals by number; tonic triads | Treble clef notes |
| Level 2 (like Grade 2) | Dotted notes and semiquavers; keys up to 3 sharps or flats; A, E and D minor; harmonic minor scales; semitones and tones | Major scales and key signatures |
| Level 3 (like Grade 3) | 6/8 and 3/8; dotted quavers; keys up to 4 sharps or flats; melodic and natural minor; major, minor and perfect intervals; triads on I, IV and V; transposition | Simple and compound time |
| Level 4 (like Grade 4) | Up to 5 sharps or flats; every interval quality including augmented and diminished; inversions; chord symbols; Roman numerals; cadences; 2/2, 9/8 and 12/8; the alto clef | Interval qualities |
| Level 5 (like Grade 5) | All keys; Roman numerals in minor keys; cadences from chord names; transposing for B♭ and E♭ instruments; 5/4 and 7/8; harder terms | Inversions, chord symbols and cadences |
Music theory quiz
Sixteen questions, new every time: theory terms, key signatures, intervals and note values. Marked by Classfern It runs on the Classfern lesson engine, and your answers never leave this device.
How long does it take to learn music theory?
The basics – reading notes and rhythms, major scales, key signatures and simple chords – take most beginners a few months of short, regular practice. Reaching a level like Grade 5 theory usually takes one to three years alongside learning an instrument. Ten minutes a day works better than one long session a week.
How do you start learning music theory on your own?
- Learn the note names on the stave and on your instrument (the stave and clefs).
- Count rhythms: semibreves, minims, crotchets and quavers (note and rest values).
- Build the major scale from its pattern of steps: T T S T T T S (T = tone, S = semitone).
- Learn key signatures one at a time, starting with G and F major.
- Build triads on each note of the scale and play them (simple chords).
- Test yourself with the quiz above and the levelled tests, a little and often.
Who invented music theory?
No single person invented music theory. Some of the oldest known writings about tuning come from ancient Mesopotamia. In ancient Greece, Pythagoras (6th century BC) is credited with finding that the octave, fifth and fourth match the simple number ratios 2:1, 3:2 and 4:3. Around 1000 AD, Guido of Arezzo helped establish the stave and the singing syllables that became do re mi.
Later theorists built on this. Johann Joseph Fux’s Gradus ad Parnassum taught counterpoint – combining independent melodies – and was used by Haydn, Mozart and Beethoven. Jean-Philippe Rameau explained harmony in terms of chords built on a root. Figured bass, from the Baroque era, is a shorthand of numbers under a bass line that tells a keyboard player which chords to fill in.
How many grades are there in music theory?
In the UK and many other countries, music theory exams have 8 grades. Both ABRSM and Trinity offer theory Grades 1 to 8, and ABRSM asks for a Grade 5 theory pass (or an alternative) before its practical Grades 6 to 8.
For GCSE and A level, theory is part of the course rather than a separate exam. Classfern is not connected with or endorsed by ABRSM, Trinity College London or the College Board; Classfern’s levels are “like Grade 1–5” and are not official exams or past papers.
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