Building Chords

The Chord class represents a collection of notes played simultaneously. The MusicTheory library supports over 40 chord types, from simple triads to complex jazz voicings.

Understanding Chords

A chord consists of:

Root Note: The fundamental note upon which the chord is built
Chord Type: Defines the intervals that make up the chord (Major, Minor7, Dom7b9, etc.)
Inversion: Which note is in the bass (root position, first inversion, etc.)
Extensions: Additional notes beyond the basic chord structure

Supported Chord Types

The library supports 40+ chord types across multiple categories:

Type	Symbol	Intervals	Example
Major	C	1-3-5	C-E-G
Minor	Cm	1-♭3-5	C-E♭-G
Diminished	C°	1-♭3-♭5	C-E♭-G♭
Augmented	C+	1-3-♯5	C-E-G♯

Type	Symbol	Intervals	Example
Major 7th	Cmaj7	1-3-5-7	C-E-G-B
Minor 7th	Cm7	1-♭3-5-♭7	C-E♭-G-B♭
Dominant 7th	C7	1-3-5-♭7	C-E-G-B♭
Half-diminished	Cø7	1-♭3-♭5-♭7	C-E♭-G♭-B♭
Diminished 7th	C°7	1-♭3-♭5-♭♭7	C-E♭-G♭-B♭♭

Type	Symbol	Notes
Major 9th	Cmaj9	C-E-G-B-D
Minor 11th	Cm11	C-E♭-G-B♭-D-F
Dominant 13th	C13	C-E-G-B♭-D-F-A

Type	Symbol	Notes
Dom7♭5	C7♭5	C-E-G♭-B♭
Dom7♯9	C7♯9	C-E-G-B♭-D♯
Alt	C7alt	C-E-G♭-G♯-B♭-D♭

Creating Chords

Basic Chord Creation

// Create root note
var c4 = new Note(NoteName.C, Alteration.Natural, 4);

// Create basic triads
var cMajor = new Chord(c4, ChordType.Major);
var cMinor = new Chord(c4, ChordType.Minor);
var cDim = new Chord(c4, ChordType.Diminished);
var cAug = new Chord(c4, ChordType.Augmented);

// Create seventh chords
var cMaj7 = new Chord(c4, ChordType.Major7);
var cm7 = new Chord(c4, ChordType.Minor7);
var c7 = new Chord(c4, ChordType.Dominant7);
var cHalfDim = new Chord(c4, ChordType.HalfDiminished7);

Extended and Altered Chords

// Extended chords
var cMaj9 = new Chord(c4, ChordType.Major9);
var cm11 = new Chord(c4, ChordType.Minor11);
var c13 = new Chord(c4, ChordType.Dominant13);

// Altered chords
var c7b5 = new Chord(c4, ChordType.Dominant7Flat5);
var c7sharp9 = new Chord(c4, ChordType.Dominant7Sharp9);
var c7alt = new Chord(c4, ChordType.Dominant7Alt);

// Suspended chords
var csus2 = new Chord(c4, ChordType.Sus2);
var csus4 = new Chord(c4, ChordType.Sus4);
var c7sus4 = new Chord(c4, ChordType.Dominant7Sus4);

Working with Chord Properties

Getting Chord Information

var cm7 = new Chord(new Note(NoteName.C, Alteration.Natural, 4), ChordType.Minor7);

// Basic properties
Note root = cm7.Root;                    // C4
ChordType type = cm7.Type;               // ChordType.Minor7
ChordInversion inv = cm7.Inversion;      // ChordInversion.Root

// Get chord symbol
string symbol = cm7.GetSymbol();         // "Cm7"

// Get notes in the chord
var notes = cm7.GetNotes().ToList();    // [C4, Eb4, G4, Bb4]

Chord Notes and Voicings

var cMaj7 = new Chord(new Note(NoteName.C, Alteration.Natural, 4), ChordType.Major7);

// Get all notes
foreach (var note in cMaj7.GetNotes())
{
    Console.WriteLine(note); // C4, E4, G4, B4
}

// Get specific note
var third = cMaj7.GetNotes().ElementAt(1);  // E4
var seventh = cMaj7.GetNotes().ElementAt(3); // B4

Chord Inversions

Inversions change which note is in the bass:

var c = new Note(NoteName.C, Alteration.Natural, 4);
var cMajor = new Chord(c, ChordType.Major);

// Create inversions
var firstInversion = cMajor.WithInversion(ChordInversion.First);   // E in bass
var secondInversion = cMajor.WithInversion(ChordInversion.Second); // G in bass

// Get bass note
var bassNote = firstInversion.GetBassNote(); // E4

// Get notes in inversion order
var inversionNotes = firstInversion.GetNotesInInversion(); // E4, G4, C5

// Slash chord notation
string slashChord = firstInversion.GetSlashChordNotation(); // "C/E"

Inversion Types

Root Position: Root in bass (C major: C-E-G)
First Inversion: Third in bass (C major: E-G-C)
Second Inversion: Fifth in bass (C major: G-C-E)
Third Inversion: Seventh in bass (C7: Bb-C-E-G) - requires 7th chord

Adding Extensions

Add extensions to existing chords using the fluent API:

var c = new Note(NoteName.C, Alteration.Natural, 4);
var cMajor = new Chord(c, ChordType.Major);

// Add a major 7th
var cMaj7 = cMajor.AddExtension(7, IntervalQuality.Major);

// Add multiple extensions (fluent API)
var cMaj9add13 = cMajor
    .AddExtension(7, IntervalQuality.Major)
    .AddExtension(9, IntervalQuality.Major)
    .AddExtension(13, IntervalQuality.Major);

// Create complex voicings
var c7sharp11 = new Chord(c, ChordType.Dominant7)
    .AddExtension(11, IntervalQuality.Augmented);

Chord Progressions

Work with chords in the context of a key:

// Define the key
var cMajorKey = new KeySignature(new Note(NoteName.C), KeyMode.Major);
var progression = new ChordProgression(cMajorKey);

// Get diatonic chords
var diatonicChords = progression.GetDiatonicChords().ToList();
// I (C), ii (Dm), iii (Em), IV (F), V (G), vi (Am), vii° (Bdim)

// Common progressions
var twoFiveOne = progression.ParseProgression("ii7 - V7 - IMaj7");
var popProgression = progression.ParseProgression("I - V - vi - IV");

// Get chord by scale degree
var dominant = progression.GetChordByDegree(5);        // G major
var submediant = progression.GetChordByDegree(6);      // A minor

Transposition

Transpose chords to different keys:

var c = new Note(NoteName.C, Alteration.Natural, 4);
var cm7 = new Chord(c, ChordType.Minor7);

// Transpose up a perfect fifth
var gm7 = cm7.Transpose(new Interval(IntervalQuality.Perfect, 5), Direction.Up);

// Transpose down a major third
var abm7 = cm7.Transpose(new Interval(IntervalQuality.Major, 3), Direction.Down);

// Verify transposition
Console.WriteLine(gm7.GetSymbol());  // "Gm7"
Console.WriteLine(abm7.GetSymbol()); // "Abm7"

Common Chord Patterns

Jazz Chord Voicings

// ii-V-I in C major
var dm7 = new Chord(new Note(NoteName.D, 4), ChordType.Minor7);
var g7 = new Chord(new Note(NoteName.G, 3), ChordType.Dominant7);
var cMaj7 = new Chord(new Note(NoteName.C, 4), ChordType.Major7);

// Altered dominant
var g7alt = new Chord(new Note(NoteName.G, 3), ChordType.Dominant7Alt);

// Extended voicings
var dm11 = new Chord(new Note(NoteName.D, 4), ChordType.Minor11);
var g13 = new Chord(new Note(NoteName.G, 3), ChordType.Dominant13);

Pop/Rock Patterns

// Power chords
var a5 = new Chord(new Note(NoteName.A, 2), ChordType.Power5);
var d5 = new Chord(new Note(NoteName.D, 3), ChordType.Power5);

// Add chords
var cAdd9 = new Chord(new Note(NoteName.C, 4), ChordType.MajorAdd9);
var fAdd9 = new Chord(new Note(NoteName.F, 4), ChordType.MajorAdd9);

// Suspended chords
var dsus2 = new Chord(new Note(NoteName.D, 4), ChordType.Sus2);
var gsus4 = new Chord(new Note(NoteName.G, 4), ChordType.Sus4);

Enharmonic Equivalents

Get enharmonically equivalent chords:

var cSharpMajor = new Chord(
    new Note(NoteName.C, Alteration.Sharp, 4), 
    ChordType.Major
);

var enharmonic = cSharpMajor.GetEnharmonicEquivalent(); // Db major
Console.WriteLine(enharmonic?.GetSymbol()); // "Db"

Best Practices

Choose appropriate chord types: Use the specific ChordType enum values rather than building chords with extensions
Consider voice leading: When creating progressions, consider the movement between chord tones
Use proper enharmonic spelling: Choose sharps or flats based on the key context
Leverage the fluent API: Chain methods for readable code

Advanced Topics

Voice Leading

Consider smooth voice movement between chords:

// Good voice leading: minimal movement
var c = new Chord(new Note(NoteName.C, 4), ChordType.Major);
var am = new Chord(new Note(NoteName.A, 3), ChordType.Minor);
var f = new Chord(new Note(NoteName.F, 4), ChordType.Major);
var g = new Chord(new Note(NoteName.G, 3), ChordType.Major);

// Common tones: C is in both C major and A minor
// Stepwise motion: E → E, G → A

Chord Substitutions

Common jazz substitutions:

// Tritone substitution
var g7 = new Chord(new Note(NoteName.G, 3), ChordType.Dominant7);
var db7 = new Chord(new Note(NoteName.D, Alteration.Flat, 3), ChordType.Dominant7);
// G7 can be substituted with Db7 (tritone away)

// Minor for major substitution
var cMajor = new Chord(new Note(NoteName.C, 4), ChordType.Major);
var aMinor = new Chord(new Note(NoteName.A, 3), ChordType.Minor);
// C major can be substituted with A minor (relative minor)

MusicTheory Help