A chord is the sound of three or more notes played simultaneously. Chords are the foundation of harmony -- they provide the emotional backdrop that melodies live inside. Understanding how chords are built from intervals is the single most important step in learning harmony.
The simplest chords are called triads because they contain exactly three notes: a root, a third, and a fifth. These names refer to the interval each note forms above the root. By changing the quality of the third and fifth (making them major, minor, diminished, or augmented), you create four fundamentally different types of triads, each with its own emotional character.
Western harmony is built on tertian harmony -- constructing chords by stacking intervals of thirds. A third is the distance of 3 or 4 semitones (half steps). By choosing between major thirds (4 semitones) and minor thirds (3 semitones), you determine the chord quality.
The Interval Stack Visualized
Major 3rd = 4 semitones
The distance from C to E, or from G to B. This wider third creates brightness.
Minor 3rd = 3 semitones
The distance from C to Eb, or from E to G. This narrower third creates darkness.
Bright, happy, resolved
The major triad is the most fundamental chord in Western music. It is built from a root, a major 3rd (4 semitones above the root), and a perfect 5th (7 semitones above the root). The major 3rd gives the chord its bright, uplifting sound. When you hear a chord that feels stable and cheerful, it is almost always a major triad.
Where you hear it
Dark, sad, introspective
The minor triad lowers the 3rd by one semitone compared to the major triad. The root and 5th stay the same, but the minor 3rd (3 semitones) creates a darker, more melancholy quality. Minor chords are used extensively for emotional depth in ballads, film scores, and minor-key compositions.
Where you hear it
Tense, unstable, dissonant
The diminished triad stacks two minor 3rds: root to minor 3rd (3 semitones), then minor 3rd to diminished 5th (6 semitones total). The diminished 5th (also called the tritone from the root) creates a strong sense of tension and instability. This chord almost always wants to resolve somewhere else, making it a powerful tool for creating movement in harmony.
Where you hear it
Mysterious, dreamlike, suspended
The augmented triad stacks two major 3rds: root to major 3rd (4 semitones), then major 3rd to augmented 5th (8 semitones total). This symmetrical structure (equal intervals) makes the chord ambiguous -- it does not clearly point to a single key or resolution. Composers use augmented triads to create a floating, otherworldly feeling.
Where you hear it
Select a root note and a triad type to see, hear, and explore any triad.
Root Note
C Major
Notes: C -- E -- G
Formula: Root + Major 3rd + Perfect 5th
Every triad is made of exactly two stacked intervals. Here is how the four types differ:
| Triad Type | Bottom 3rd | Top 3rd | 5th Quality | Total Semitones | Sound |
|---|---|---|---|---|---|
| Major | Major 3rd (4) | Minor 3rd (3) | Perfect 5th | 0, 4, 7 | Bright, stable |
| Minor | Minor 3rd (3) | Major 3rd (4) | Perfect 5th | 0, 3, 7 | Dark, emotional |
| Diminished | Minor 3rd (3) | Minor 3rd (3) | Diminished 5th | 0, 3, 6 | Tense, unstable |
| Augmented | Major 3rd (4) | Major 3rd (4) | Augmented 5th | 0, 4, 8 | Dreamlike, floating |
Notice that both the major and minor triads share the same perfect 5th. The only difference is the 3rd: major 3rd (4 semitones) for major, minor 3rd (3 semitones) for minor. This single semitone difference is what separates a happy-sounding chord from a sad one. The 3rd is the most important note in any chord for determining its emotional quality.
Similarly, diminished and augmented triads both modify the 5th. The diminished triad flattens it (creating tension through the tritone), while the augmented triad raises it (creating an ethereal, unresolved feeling). Every chord quality comes down to these interval choices.
In any major scale, each scale degree naturally produces a specific triad type. This pattern is the same in every key: I-ii-iii-IV-V-vi-vii-dim. Understanding this pattern helps you predict which chords belong together.
| Degree | Roman | Type | In C Major |
|---|---|---|---|
| 1st | I | Major | C |
| 2nd | ii | Minor | Dm |
| 3rd | iii | Minor | Em |
| 4th | IV | Major | F |
| 5th | V | Major | G |
| 6th | vi | Minor | Am |
| 7th | vii | Diminished | Bdim |
Remember: The numbers in brackets represent semitones above the root. A semitone is the smallest step on a piano (from any key to the very next key). So [0, 4, 7] means root, 4 semitones up, and 7 semitones up from the root.