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A triad is a three-note chord built by stacking two 3rd intervals above a root note. A major triad consists of a major 3rd plus a perfect 5th, while a minor triad has a minor 3rd plus a perfect 5th. These two types are the foundation of tonal harmony with distinctly different characters—major sounds bright, minor sounds dark.
Build major and minor triads above various roots on staff and keyboard, using interval knowledge to verify. Listen to major vs. minor triads and practice identifying them by ear.
Building a triad with a major 3rd and major 5th (there is no 'major 5th'—the 5th is perfect). Thinking minor triads have a diminished 5th (they have perfect 5th). Confusing letter-name distances with interval quality.
You already know how to measure intervals precisely — both the letter-name distance and the quality (major, minor, perfect). A triad puts that knowledge to work by stacking two thirds above a root. The root is the bottom note and gives the chord its name. The middle note is a third above the root, and the top note — the fifth — is a third above the middle note, which makes it a fifth above the root. Three notes, two stacked thirds: that is the definition of a triad.
The difference between a major triad and a minor triad comes down to a single semitone. A major triad uses a major third from root to middle note (4 semitones), then a minor third from middle to top (3 semitones), giving a total of 7 semitones from root to fifth. A minor triad uses a minor third from root to middle note (3 semitones), then a major third from middle to top (4 semitones), also giving 7 semitones from root to fifth. Both have a perfect fifth spanning the outside two notes; the only difference is which note sits in the middle. To build C major: C up a major third to E, then E up a minor third to G — result: C-E-G. To build C minor: C up a minor third to E♭, then E♭ up a major third to G — result: C-E♭-G.
This structure explains why major and minor triads sound so different despite sharing the same outer interval. The perfect fifth is acoustically stable and consonant in both cases. What creates the perceptual contrast is the placement of the third. In a major triad, the major third is on the bottom, which means the chord's interior emphasis falls on a brighter, higher-tension interval. In a minor triad, the minor third is on the bottom, producing a darker interior quality. Experienced listeners often describe this as major sounding "open" or "bright" and minor sounding "closed" or "dark," though these associations vary across cultures and contexts.
A common error is to think minor triads have a diminished fifth — they do not. Both major and minor triads span a perfect fifth (7 semitones). The diminished triad, which you will encounter next, is different precisely because its fifth is diminished (6 semitones). When checking your triad construction, always verify the outer interval first: if it is not a perfect fifth, something has gone wrong. Then check the quality of the third to determine major or minor. This two-step check — fifth first, then third — is the fastest way to catch errors when building triads at the keyboard or on staff paper.
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