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A triad is a three-note chord built by stacking two thirds. The four triad types differ in interval content: major (major third + minor third, e.g., C-E-G), minor (minor third + major third, e.g., C-E♭-G), diminished (minor third + minor third, e.g., C-E♭-G♭), and augmented (major third + major third, e.g., C-E-G♯). The lowest note in root position is the root, the middle note is the third, and the top note is the fifth. Triads are the fundamental building blocks of Western tonal harmony.
Build all four triad types starting on C by adjusting the third and fifth. Then build triads on every note of the major scale to discover which types naturally occur. Play triads on an instrument and sing through them to internalize their qualities.
A triad is not simply three notes played together — it is a specific arrangement of intervals that gives each chord its quality and character. You have already worked with intervals (major, minor, perfect), so the four triad types are best understood as combinations of two stacked thirds. The choice of which thirds to stack produces four distinct sounds, each with a name and a set of harmonic associations.
Start with the major triad: a major third (4 half steps) on the bottom, a minor third (3 half steps) on top. C-E-G is the clearest example: C to E is a major third, E to G is a minor third. The result sounds stable and bright — the triad that defines a major key. Now lower the middle note by a half step (E to E♭) and you have C-E♭-G: a minor triad, with the intervals reversed (minor third on bottom, major third on top). The outer frame — root to fifth — is the same (both span a perfect fifth), but the inner division has flipped, and the character shifts noticeably toward something darker or more melancholy.
The diminished triad (C-E♭-G♭) stacks two minor thirds, compressing the outer interval to a diminished fifth (also called a tritone). This creates an unstable, tense sound that demands resolution — you hear it most often on the seventh scale degree of a major key, where it pulls strongly toward the tonic. The augmented triad (C-E-G♯) stacks two major thirds, stretching the outer interval to an augmented fifth. This creates a shimmering, ambiguous quality that composers use for coloristic or disorienting effects.
An important precision: the 'third' and 'fifth' of a triad are named for their interval above the root, not for their position in the three-note stack. The middle note is always a third above the root, and the top note is always a fifth above the root (even when the fifth is diminished or augmented). This naming is consistent regardless of how the chord is rearranged (inverted).
When you build triads on every scale degree of a major scale, you will discover that major, minor, and diminished triads all appear naturally — augmented does not. This pattern of triad qualities across the scale is called diatonic harmony, and it is the next major step in understanding how tonal music is organized. Knowing triad structure cold will make that topic much easier to grasp.
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