Major triad

A major triad is a three-note chord built from a root, a major third above the root, and a perfect fifth above the root (a major third with a minor third stacked on top). In AP Music Theory it's labeled with uppercase Roman numerals (I, IV, V in major keys) and is the most stable triad quality.

What is Major triad?

A major triad is the simplest version of "a chord" in tonal music. Take any note as the root, add the note a major third above it, then add the note a perfect fifth above the root. C-E-G is the classic example. Another way to hear the structure is as two stacked thirds, a major third on the bottom (C to E) and a minor third on top (E to G). That bottom third is what gives the chord its bright, settled sound.

On the AP exam, you'll work with major triads in every direction at once. You spell them on the staff, identify them by ear, label them with uppercase Roman numerals, and stack them in four-voice (SATB) texture. In a major key, the triads built on scale degrees 1, 4, and 5 are major (I, IV, V), and those three chords carry most of the harmonic weight in the music you'll analyze and write. In minor keys, V becomes major too, because you raise the leading tone.

Why Major triad matters in AP Music Theory

Triad qualities are the core content of Unit 3 (Music Fundamentals III: Triads and Seventh Chords), and the major triad is the reference point you measure every other quality against. A minor triad is a major triad with a lowered third. An augmented triad is a major triad with a raised fifth. If you can't spell and hear a major triad instantly, every other chord type gets harder.

It also never goes away. Units 4 and 5 build chord progressions and voice-leading rules on top of triads, and Unit 7's secondary dominants depend on you recognizing that a dominant-function chord must be major quality. When you see an unexpected major triad in analysis, like E major in the key of C, that's often your clue that a secondary dominant or tonicization is happening. The major triad is also where Roman numeral conventions start, since uppercase numerals literally mean "this triad is major."

How Major triad connects across the course

Augmented triad (Unit 3)

An augmented triad is a major triad whose fifth has been raised a half step, so it's built from two major thirds instead of major-plus-minor. On quality-ID questions, the third sounds the same in both chords; the fifth is what gives the augmented triad away.

Chord progression (Units 4-5)

Progressions in a major key lean on the three major triads, I, IV, and V. Tonic, predominant, and dominant function all have a major triad at the center, so progression analysis is largely a matter of tracking where these chords sit and where they want to go.

Secondary dominant (Unit 7)

A secondary dominant is a major triad (or dominant seventh) borrowed to point at a chord other than tonic. Spotting one starts with noticing a major-quality triad where the key signature says there shouldn't be one, like D major in C major acting as V/V.

Voice-Leading Rules (Units 4-5)

Part writing asks you to spread a major triad across four voices, which means deciding what to double (usually the root) and occasionally what to omit. The triad is the raw material; voice leading is the set of rules for moving from one triad to the next without parallel fifths or octaves.

Is Major triad on the AP Music Theory exam?

Major triads show up in both halves of the exam. In the multiple-choice section, you'll identify triad quality by ear in aural questions and by sight in score-based questions, often choosing among major, minor, diminished, and augmented. In the free-response section, the part-writing questions (realizing figured bass and Roman numerals in four voices) assume you can spell any major triad in any key instantly, and the harmonic dictation FRQ asks you to hear major-quality chords and label them with the right Roman numerals. Even sight singing touches it, since melodies frequently arpeggiate the tonic or dominant triad. The skill being tested is speed and accuracy, not deep interpretation. You either spell C-sharp major correctly under time pressure or you don't, so drill spelling in every key.

Major triad vs Minor triad

Both chords have a perfect fifth between root and fifth, so the outer interval sounds identical. The only difference is the third. A major triad has a major third above the root (C-E-G); a minor triad lowers that third a half step (C-Eb-G). By ear, focus on the quality of the bottom third, since that single half step is the entire distinction. On Roman numerals, major triads get uppercase (IV) and minor triads get lowercase (iv).

Key things to remember about Major triad

• A major triad is built from a root, a major third above the root, and a perfect fifth above the root, like C-E-G.

• Thought of as stacked thirds, a major triad is a major third on the bottom with a minor third on top.

• In a major key, the triads on scale degrees 1, 4, and 5 (I, IV, and V) are major, and uppercase Roman numerals always signal major quality.

• In minor keys, raising the leading tone turns the v chord into a major V, which is what makes dominant function work.

• An unexpected major triad outside the key is a common signal of a secondary dominant or tonicization in Unit 7 analysis.

• In SATB part writing, you usually double the root of a major triad and follow voice-leading rules when moving to the next chord.

Frequently asked questions about Major triad

What is a major triad in AP Music Theory?

It's a three-note chord made of a root, a major third above the root, and a perfect fifth above the root, such as C-E-G or G-B-D. It's the most stable chord quality and the foundation for Roman numeral analysis and part writing.

What's the difference between a major triad and a minor triad?

Only the third changes. A major triad has a major third above the root (C-E-G), while a minor triad lowers that third a half step (C-Eb-G). The perfect fifth is identical in both, which is why your ear should zero in on the bottom third.

Is the major triad always the tonic chord?

No. In a major key, I, IV, and V are all major triads, and in minor keys the dominant V becomes major once you raise the leading tone. Major quality tells you the chord's sound, not its function; the Roman numeral and key context tell you the function.

How do I tell a major triad from an augmented triad by ear?

Listen to the fifth. Both chords start with a major third, but the augmented triad raises the fifth a half step, stacking two major thirds and creating an unstable, unresolved sound. The major triad's perfect fifth sounds settled by comparison.

Which Roman numerals are major triads in a major key?

I, IV, and V, all written in uppercase. The triads on scale degrees 2, 3, and 6 are minor (ii, iii, vi), and the triad on scale degree 7 is diminished (vii°).