What Is a Chord?

Department of Music | Stage: Nigredo (Beginner) | Duration: 25 minutes

Objectives

After this lesson, you will be able to:

Define what an interval is and name the intervals from unison through octave
Explain the difference between a major triad and a minor triad
Build any major or minor chord from its root using intervals
Understand why some combinations of notes sound stable and others tense

1. Intervals — The Building Blocks

Before you can understand chords, you need to understand intervals. An interval is the distance in pitch between two notes. Every relationship in music starts here.

Starting from any note, the intervals within one octave are:

Interval	Semitones	Example (from C)	Sound Quality
Unison	0	C to C	Identity
Minor 2nd	1	C to Db	Tense, dissonant
Major 2nd	2	C to D	Bright step
Minor 3rd	3	C to Eb	Sad, dark
Major 3rd	4	C to E	Happy, bright
Perfect 4th	5	C to F	Open, hollow
Tritone	6	C to F#/Gb	Unstable, restless
Perfect 5th	7	C to G	Strong, stable
Minor 6th	8	C to Ab	Bittersweet
Major 6th	9	C to A	Warm
Minor 7th	10	C to Bb	Bluesy
Major 7th	11	C to B	Bright tension
Octave	12	C to C (higher)	Same note, higher

A semitone (also called a half step) is the smallest distance between two notes in Western music. On a piano, it is the distance from one key to the very next key (white or black). On a guitar, it is one fret.

Practice Exercise

Pick any note on a piano or guitar. Starting from that note, count up the semitones and name each interval as you go. Say them out loud: “One semitone, minor second. Two semitones, major second.” Go all the way to the octave (12 semitones). Repeat from a different starting note.

2. Stacking Intervals — How Chords Are Born

A chord is three or more notes sounded together. The simplest chord is a triad — three notes built by stacking two intervals of a third on top of each other.

Here is the key insight: a chord is not a random collection of notes. It is intervals stacked in a specific pattern from a root note.

To build a triad:

Start with your root note (this gives the chord its name)
Add a note a third above the root
Add a note a third above that second note (which is a fifth above the root)

The type of thirds you stack determines whether the chord is major or minor.

3. Major Triads — The Bright Sound

A major triad is built by stacking:

Major 3rd (4 semitones) from root to middle note
Minor 3rd (3 semitones) from middle note to top note
Total: root to top = Perfect 5th (7 semitones)

Example — C Major:

Root: C
Major 3rd up: E (4 semitones from C)
Minor 3rd up from E: G (3 semitones from E)
The chord: C - E - G

Major chords sound bright, happy, resolved. When you hear a triumphant fanfare or a sunny pop chorus, major chords are doing the work.

Practice Exercise

Build the following major triads on paper or on your instrument. For each, start at the root, count 4 semitones up (major 3rd), then 3 more semitones up (minor 3rd):

G Major (G - ? - ?)
D Major (D - ? - ?)
A Major (A - ? - ?)

Answers: G-B-D, D-F#-A, A-C#-E.

4. Minor Triads — The Dark Sound

A minor triad reverses the stacking order:

Minor 3rd (3 semitones) from root to middle note
Major 3rd (4 semitones) from middle note to top note
Total: root to top = still a Perfect 5th (7 semitones)

Example — A Minor:

Root: A
Minor 3rd up: C (3 semitones from A)
Major 3rd up from C: E (4 semitones from C)
The chord: A - C - E

Minor chords sound dark, sad, introspective. Ballads, blues, and moody film scores lean on minor chords.

Notice something remarkable: both major and minor triads span a perfect fifth from root to top. The only difference is whether the major third comes first or second. That tiny shift — one semitone in the middle note — transforms the entire emotional character.

Practice Exercise

Build these minor triads. Start at the root, count 3 semitones (minor 3rd), then 4 more (major 3rd):

E Minor (E - ? - ?)
D Minor (D - ? - ?)
B Minor (B - ? - ?)

Answers: E-G-B, D-F-A, B-D-F#.

5. Consonance and Dissonance — Why Chords Sound the Way They Do

Why does a major chord sound “happy” and a minor chord sound “sad”? Why does a tritone sound unsettling?

The answer lies in frequency ratios. When two notes vibrate, their sound waves interact:

Consonant intervals have simple frequency ratios. A perfect fifth (3:2) and a perfect fourth (4:3) sound stable because their waves align frequently, reinforcing each other.
Dissonant intervals have complex ratios. A minor second (16:15) or tritone (45:32) create waves that clash, producing a sense of tension or roughness.

A major triad combines three consonant intervals (major 3rd, minor 3rd, perfect 5th), producing a stable, resolved sound. A minor triad uses the same intervals in a different arrangement, which is still consonant but with a darker quality due to the lower third.

Dissonance is not “bad.” Music needs tension to create movement. A chord that feels tense wants to resolve to a stable chord — and that pull from tension to resolution is what makes music feel alive.

Practice Exercise

On your instrument, play these pairs and listen to the difference:

C and G together (perfect 5th — consonant)
C and Db together (minor 2nd — dissonant)
C-E-G (C major — stable)
C-E-Gb (unstable — the fifth is diminished)

Notice how your ear wants the dissonant sounds to “go somewhere.” That desire for resolution is the engine of harmony.

6. Beyond Triads — A Preview

Triads are only the beginning. By stacking more thirds, you get richer chords:

Chord Type	Formula	Example (from C)	Sound
Major triad	1 - 3 - 5	C - E - G	Bright, stable
Minor triad	1 - b3 - 5	C - Eb - G	Dark, stable
Dominant 7th	1 - 3 - 5 - b7	C - E - G - Bb	Bluesy, wants to resolve
Major 7th	1 - 3 - 5 - 7	C - E - G - B	Dreamy, jazzy
Minor 7th	1 - b3 - 5 - b7	C - Eb - G - Bb	Mellow, smooth

Every one of these is built from the same principle: stacking intervals from a root. Once you internalize this, you can construct any chord from scratch — no memorization required.

Key Terms

Term	Definition
Interval	The distance in pitch between two notes, measured in semitones
Semitone	The smallest interval in Western music (one fret on guitar, one key on piano)
Triad	A three-note chord built by stacking two thirds
Major triad	Root + major 3rd (4 semitones) + minor 3rd (3 semitones)
Minor triad	Root + minor 3rd (3 semitones) + major 3rd (4 semitones)
Consonance	Intervals with simple frequency ratios that sound stable
Dissonance	Intervals with complex frequency ratios that create tension
Root	The note a chord is built from and named after

Self-Check Assessment

1. How many semitones are in a major 3rd? A minor 3rd?

Major 3rd = 4 semitones. Minor 3rd = 3 semitones.

2. What is the difference in construction between C major and C minor?

C major = C-E-G (major 3rd then minor 3rd). C minor = C-Eb-G (minor 3rd then major 3rd). The middle note (E vs Eb) differs by one semitone.

3. Build an F major triad from scratch.

Root: F. Major 3rd up (4 semitones): A. Minor 3rd up from A (3 semitones): C. F major = F-A-C.

4. Why does a perfect fifth sound more stable than a tritone?

A perfect fifth has a simple frequency ratio (3:2), so the sound waves reinforce each other. A tritone has a complex ratio (45:32), creating wave interference that sounds tense and unstable.

Pass criteria: Build any major or minor triad from a given root note using interval counting, and explain why the triad sounds major or minor based on the order of stacked thirds.

Research Basis

Intervals are the atomic unit of Western harmony — all chord theory derives from interval stacking
The major/minor distinction from third ordering is universal across tonal music systems
Consonance correlates with frequency ratio simplicity (Helmholtz, 1863; Plomp & Levelt, 1965)
Sources: Music theory pedagogy consensus, Streeling Department of Music curriculum
Belief state: T(0.90) F(0.02) U(0.05) C(0.03)