A triad is a three-note chord built by stacking thirds. It's the fundamental unit of harmony — every chord you've ever played or heard is either a triad or an extension of one.

How Triads Are Built

A triad is constructed from a root, a third (3 or 4 half steps above the root), and a fifth (7 half steps above the root, usually). The quality of the triad depends on whether the third is major or minor.

The Four Triad Types

Major Triad

Built with a major third (4 half steps) + minor third (3 half steps) on top.

Formula: 1 – 3 – 5

Example: C major = C – E – G

Sound: bright, happy, stable

Minor Triad

Built with a minor third (3 half steps) + major third (4 half steps) on top.

Formula: 1 – ♭3 – 5

Example: A minor = A – C – E

Sound: dark, melancholic, introspective

Diminished Triad

Built with two minor thirds stacked (3 + 3 half steps).

Formula: 1 – ♭3 – ♭5

Example: B diminished = B – D – F

Sound: tense, unstable, dissonant — wants to resolve

Augmented Triad

Built with two major thirds stacked (4 + 4 half steps).

Formula: 1 – 3 – #5

Example: C augmented = C – E – G#

Sound: mysterious, ambiguous, unsettled

Inversions

A triad is in root position when the root is the lowest note. When you rearrange the notes so a different note is on the bottom, you have an inversion:

  • Root position: C – E – G (root on bottom)
  • First inversion: E – G – C (third on bottom)
  • Second inversion: G – C – E (fifth on bottom)

Inversions let you voice chords smoothly — moving to the nearest inversion of the next chord instead of jumping around. This is called voice leading and is one of the core skills in arranging and writing chord progressions that feel connected.

Triads in a Key

Every major scale produces seven triads — one built on each scale degree. In C major:

DegreeChordQuality
ICMajor
iiDmMinor
iiiEmMinor
IVFMajor
VGMajor
viAmMinor
vii°BdimDiminished

This pattern of major, minor, minor, major, major, minor, diminished is the same in every major key — only the note names change.