Theory as a practical language
Music theory is the language we use to describe musical ideas. It helps you make choices and communicate them to other musicians. It takes practice to become fluent, and you can make wonderful music while you are still learning it.
This lesson follows Jon Pike’s Practical Music Theory — A Field Guide for Modern Musicians, written from his experience in songwriting, production and performance. It focuses on the Western tonal language commonly used in modern pop music. Other musical traditions use different systems.
Work through it in chunks, with an instrument nearby. Listen for these ideas in songs and use them in your own writing: that is where the vocabulary starts to become useful.
Terms and context
One word can describe several different things. “C major” might mean a chord, a scale or a key. “One” might mean a scale degree, a chord number or a rhythm count. Say which you mean when the context is unclear.
For example: the note C, the C major chord, the major chord quality, the key of C major, a major third interval, the 1 chord, and beat 1.
The colours echo the guide’s visual vocabulary; the words identify the meaning too. A piano “key” and a musical “key” are different things, and “tone” can mean either an interval or the character of a sound.
Notes and intervals
In twelve-tone equal temperament, there are twelve pitch classes before the pattern repeats: C, C♯, D, D♯, E, F, F♯, G, G♯, A, A♯, B. Moving to the next occurrence of a note gives an octave. In common scientific pitch notation, middle C is C4.
A sharp raises a note by one semitone; a flat lowers it by one semitone. C♯ and D♭ share a piano key, but the spelling depends on the musical context. Sharps and flats can refer to white keys too: E♯ sounds like F.
An interval is the distance between two notes. A semitone, or half step, is one adjacent piano-key movement, including black keys. A whole tone, or whole step, is two semitones. An octave is twelve semitones.
| Interval | Semitones | Example above C |
|---|---|---|
| Major 2nd | 2 | D |
| Minor 3rd | 3 | E♭ |
| Major 3rd | 4 | E |
| Perfect 4th | 5 | F |
| Perfect 5th | 7 | G |
| Minor 6th | 8 | A♭ |
| Major 6th | 9 | A |
| Minor 7th | 10 | B♭ |
| Major 7th | 11 | B |
| Octave | 12 | C |
| Major 9th | 14 | D, an octave higher |
Chords, variations and extensions
A chord combines notes around a root. On a chord chart, C means C major; Cm means C minor. The root names the chord, even when another note is in the bass.
A triad has three notes. A major triad uses a root, major third and perfect fifth; a minor triad lowers that third by one semitone. A power chord omits the third, leaving the root and fifth, often with an octave doubled.
| Symbol | Construction | Notes in C |
|---|---|---|
| C | Major triad | C E G |
| Cm | Minor triad | C E♭ G |
| C5 | Root and fifth; optional octave | C G (C) |
| C6 | Major triad plus major sixth | C E G A |
| Csus2 | Replace the third with a second | C D G |
| Csus4 | Replace the third with a fourth | C F G |
| Cadd9 | Major triad plus ninth | C E G D |
| Cadd4 | Major triad plus fourth | C E F G |
| Cm7 | Minor triad plus minor seventh | C E♭ G B♭ |
| Cmaj7 | Major triad plus major seventh | C E G B |
| C7 | Major triad plus minor seventh | C E G B♭ |
“Sus” replaces the third, while “add” keeps it and adds another note. A ninth is an octave above a second. Chord tones can move between octaves, and players sometimes omit the fifth: C–E–A is a useful reduced voicing of C6.
Jon often experiments with add4 on the 5 chord. Treat that as an arranging choice: the added fourth and major third create a close tension that changes with the voicing.
Voicings and inversions
A voicing is the way chord notes are arranged, spaced and doubled. C–E–G and C–G–E use the same pitch classes but have different spacing and feel. Try moving one note up an octave or doubling a note in another register.
An inversion puts a chord tone other than the root in the bass. C major in root position has C underneath; its first inversion has E underneath; its second inversion has G underneath.
| Position | Example | Slash-chord name |
|---|---|---|
| Root position | C E G | C |
| First inversion | E G C | C/E |
| Second inversion | G C E | C/G |
The guide uses “(a)” and “(b)” for first and second inversions. Slash symbols are another common way to specify the bass. Seventh chords have a third inversion as well.
Progressions and substitutions
A chord progression is a sequence of chords. C–G–Am–F is a familiar pop example. A song can repeat one progression or give its verse, chorus and bridge different sequences.
Substitution gives you another option under the same melody. In Jon’s example, Bm–A–D–G becomes Bm–A–D–Em. G major (G–B–D) and E minor (E–G–B) share two notes, so the change can feel connected while shifting the colour.
Shared notes make a substitution worth trying, but the melody and musical context still decide whether it works. Listen for clashes and for changes in energy.
Scales, keys and relative minor
A scale is an ordered family of notes. A key is the tonal landscape of a piece, with a home note or chord called the tonic. The home chord often feels like a point of resolution.
The major scale follows whole, whole, half, whole, whole, whole, half steps. C major is C–D–E–F–G–A–B. C natural minor is C–D–E♭–F–G–A♭–B♭.
Scale degrees name positions: in C major, degree 1 is C, degree 3 is E and degree 6 is A. Jon recommends getting familiar with how each degree sounds and feels, so you can ask a collaborator to “end on the one” rather than calculate every note name first.
| Scale | Degrees relative to the major scale |
|---|---|
| Major | 1 2 3 4 5 6 7 |
| Natural minor | 1 2 ♭3 4 5 ♭6 ♭7 |
| Major pentatonic | 1 2 3 5 6 |
| Minor pentatonic | 1 ♭3 4 5 ♭7 |
| Harmonic minor | 1 2 ♭3 4 5 ♭6 7 |
| Minor blues | 1 ♭3 4 ♭5 5 ♭7 |
Relative major and natural minor keys share their notes but have different tonal centres. C major and A minor both use the white-key notes. The relative minor starts on the major scale’s sixth degree, three semitones below the major tonic.
A key signature records the usual sharps or flats; a key also involves which note feels like home. Notes outside the signature can appear without changing the overall key.
Relative chord numbers
Nashville numbers describe chords by the scale degree of their root. In a major key, the basic diatonic pattern is 1, 2-, 3-, 4, 5, 6-, 7°. A bare number means major, “-” means minor and “°” means diminished.
In C, 1–4–6-–5 means C–F–Am–G. In G, the same chart means G–C–Em–D. Transposing moves the whole piece by the same interval, so you can change the singer’s range without rewriting its relationships.
Jon’s working convention: agree to number from the major or relative major, even when a song feels minor. With C as the agreed reference, an A-minor home chord is 6-. Other musicians number from the minor tonic and call it 1-. Say which system you are using before rehearsing.
Common variations include 1maj7, 2-7, 3-7, 4add9 or 4sus2, 5sus4 and 6-7.
Read the Nashville Number System subject → · Open the Nashville Numbers tool →
Diatonic and non-diatonic chords
Diatonic means drawn from the notes of the key’s scale. Non-diatonic notes and chords go outside that set. Those changes can add tension, surprise or a distinctive colour.
| Number in C | Chord | Note outside C major |
|---|---|---|
| ♭7 | B♭ major | B♭ |
| 2 | D major | F♯ |
| 3 | E major | G♯ |
| 4- | F minor | A♭ |
| 5- | G minor | B♭ |
Two of Jon’s favourite moves are 4- resolving to 1, and 3 leading to 6-. In C, try Fm–C for a dramatic resolution, or E–Am for a pull towards the relative minor.
Chord cheat sheets
The four familiar pop chords are 1, 4, 5 and 6-. Change their order, rhythm and voicing to explore different songs. These tables adapt the guide’s quick references using spellings that follow each key.
| Major / relative minor | 1 | 4 | 5 | 6- |
|---|---|---|---|---|
| C major / A minor | C | F | G | Am |
| D♭ major / B♭ minor | D♭ | G♭ | A♭ | B♭m |
| D major / B minor | D | G | A | Bm |
| E♭ major / C minor | E♭ | A♭ | B♭ | Cm |
| E major / C♯ minor | E | A | B | C♯m |
| F major / D minor | F | B♭ | C | Dm |
| F♯ major / D♯ minor | F♯ | B | C♯ | D♯m |
| G major / E minor | G | C | D | Em |
| A♭ major / F minor | A♭ | D♭ | E♭ | Fm |
| A major / F♯ minor | A | D | E | F♯m |
| B♭ major / G minor | B♭ | E♭ | F | Gm |
| B major / G♯ minor | B | E | F♯ | G♯m |
| Major / relative minor | 1 | 2- | 3- | 4 | 5 | 6- | 7° |
|---|---|---|---|---|---|---|---|
| C major / A minor | C | Dm | Em | F | G | Am | B° |
| D♭ major / B♭ minor | D♭ | E♭m | Fm | G♭ | A♭ | B♭m | C° |
| D major / B minor | D | Em | F♯m | G | A | Bm | C♯° |
| E♭ major / C minor | E♭ | Fm | Gm | A♭ | B♭ | Cm | D° |
| E major / C♯ minor | E | F♯m | G♯m | A | B | C♯m | D♯° |
| F major / D minor | F | Gm | Am | B♭ | C | Dm | E° |
| F♯ major / D♯ minor | F♯ | G♯m | A♯m | B | C♯ | D♯m | E♯° |
| G major / E minor | G | Am | Bm | C | D | Em | F♯° |
| A♭ major / F minor | A♭ | B♭m | Cm | D♭ | E♭ | Fm | G° |
| A major / F♯ minor | A | Bm | C♯m | D | E | F♯m | G♯° |
| B♭ major / G minor | B♭ | Cm | Dm | E♭ | F | Gm | A° |
| B major / G♯ minor | B | C♯m | D♯m | E | F♯ | G♯m | A♯° |
| Major / relative minor | 1 | 2- | 2 | 3- | 3 | 4 | 4add9 | 4- | 5 | 5sus | 5- | 6- | ♭7 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| C major / A minor | C | Dm | D | Em | E | F | Fadd9 | Fm | G | Gsus4 | Gm | Am | B♭ |
| D♭ major / B♭ minor | D♭ | E♭m | E♭ | Fm | F | G♭ | G♭add9 | G♭m | A♭ | A♭sus4 | A♭m | B♭m | C♭ |
| D major / B minor | D | Em | E | F♯m | F♯ | G | Gadd9 | Gm | A | Asus4 | Am | Bm | C |
| E♭ major / C minor | E♭ | Fm | F | Gm | G | A♭ | A♭add9 | A♭m | B♭ | B♭sus4 | B♭m | Cm | D♭ |
| E major / C♯ minor | E | F♯m | F♯ | G♯m | G♯ | A | Aadd9 | Am | B | Bsus4 | Bm | C♯m | D |
| F major / D minor | F | Gm | G | Am | A | B♭ | B♭add9 | B♭m | C | Csus4 | Cm | Dm | E♭ |
| F♯ major / D♯ minor | F♯ | G♯m | G♯ | A♯m | A♯ | B | Badd9 | Bm | C♯ | C♯sus4 | C♯m | D♯m | E |
| G major / E minor | G | Am | A | Bm | B | C | Cadd9 | Cm | D | Dsus4 | Dm | Em | F |
| A♭ major / F minor | A♭ | B♭m | B♭ | Cm | C | D♭ | D♭add9 | D♭m | E♭ | E♭sus4 | E♭m | Fm | G♭ |
| A major / F♯ minor | A | Bm | B | C♯m | C♯ | D | Dadd9 | Dm | E | Esus4 | Em | F♯m | G |
| B♭ major / G minor | B♭ | Cm | C | Dm | D | E♭ | E♭add9 | E♭m | F | Fsus4 | Fm | Gm | A♭ |
| B major / G♯ minor | B | C♯m | C♯ | D♯m | D♯ | E | Eadd9 | Em | F♯ | F♯sus4 | F♯m | G♯m | A |
Try maj7 on 1 or 4, m7 on the minor chords, and dominant 7 on 5. A dominant 7 on 1 introduces a note outside the major scale. The 7° triad is diminished; changing it to minor changes its notes.
Rhythm, tempo and time signatures
Rhythm describes when notes happen and how long they last. Bars organise those durations, and phrases group bars into larger ideas. Tempo states how fast a specified note value repeats: always check which note value the BPM refers to.
At quarter note = 60 BPM, each quarter lasts one second. At quarter note = 120 BPM, it lasts half a second. The Nashville tool keeps that quarter-note BPM convention across its time signatures.
A time signature’s top number tells you how many of the bottom number’s note value fill a bar. In 4/4, a bar has four quarter notes; in 3/4, three. In 6/8, it has six eighth notes, usually felt in two groups of three with emphasis on counts 1 and 4.
At quarter note = 120 BPM, a 6/8 bar lasts 1.5 seconds. Some scores instead mark dotted-quarter BPM for 6/8, so check the tempo marking before comparing numbers.
| Meter | Quarter-note equivalents per bar | Eighth notes per bar | Sixteenth notes per bar |
|---|---|---|---|
| 4/4 | 4 | 8 | 16 |
| 3/4 | 3 | 6 | 12 |
| 5/4 | 5 | 10 | 20 |
| 6/4 | 6 | 12 | 24 |
| 7/4 | 7 | 14 | 28 |
| 6/8 | 3 | 6 | 12 |
| 12/8 | 6 | 12 | 24 |
A whole note always lasts four quarter notes. A 6/8 bar lasts three quarter notes, so a dotted half note fills it. A whole-bar rest can represent a complete bar in different meters.
Communicating a rhythmic idea
For sixteenth-note subdivisions in 4/4, count 1 e & a · 2 e & a · 3 e & a · 4 e & a. That gives sixteen precise positions in a bar. In 6/8, you can count sixteenth notes as 1 & 2 & 3 & 4 & 5 & 6 &, keeping the larger 3 + 3 grouping.
Jon’s collaboration example is to bring the third chord in on the “a” of beat 4 in bar 2. That gives the band a specific timing to try. For a drum idea, you might ask for kick on 1, the “a” of 1 and the “&” of 2, with snare on 2 and 4.
The downbeat is the first beat of a bar. “&” counts are commonly called offbeats or upbeats. Agree on the bar and count when you give a timing instruction.
Put the language to work
Pick a song you know. Find the chord that feels like home, number its progression, then try a substitution, a new inversion or a different rhythm. Listen to what each change does before deciding whether it fits.
Go deeper into Nashville chart notation →
About the author
Jon Pike is a songwriter, producer, performer and music educator. His guide grew out of using theory in writing, recording and performance, with the aim of helping musicians communicate clearly and unlock creative choices.
Adapted from Jon Pike’s field guide for this web lesson. Examples and reference tables have been clarified for standard note spelling and notation. The original PDF includes the author’s full text and draft rhythm section.