Start with one major scale, stack thirds on every scale degree, and discover the chord pattern that repeats in every major key.
Diatonic simply means that the notes belong to the key we are using. In C major, we use only C, D, E, F, G, A, and B. Build a triad on each note without leaving that seven-note collection.
Starting on C gives C–E–G. Starting on D gives D–F–A. The same stacking process continues on every scale degree.
We are always stacking every other note, but the distances between those notes are not identical. The major scale itself determines whether each resulting triad is major, minor, or diminished.
You do not choose the chord qualities separately. If you stay inside the major scale, the seven qualities appear automatically in the same order every time.
Click any chord below. The keyboard will highlight its three notes. Notice that every chord uses only notes from the C-major scale.
C major: C–E–G. This is the I chord—the tonal center of the key.
Major – minor – minor – Major – Major – minor – diminished. This quality pattern is one of the most useful things to memorize in tonal harmony.
Chord names change when the key changes. Roman numerals do not. They tell us which scale degree the chord is built on and what quality it has.
Uppercase Roman numerals mean major triads.
Lowercase Roman numerals mean minor triads.
The small circle tells us the triad is diminished.
Suppose a progression is I–vi–IV–V. In C major that means C–Am–F–G. In G major it means G–Em–C–D. The chord names changed, but the harmonic relationships stayed the same.
A chord's function describes the job it tends to perform in a key. These are useful families rather than rigid rules; context and voice leading can change how a chord behaves.
Rest, stability, home. I is the strongest tonic. iii and vi often share tonic notes and can sometimes prolong or substitute for tonic harmony.
Movement away from home. These chords commonly prepare the dominant and create forward motion toward V.
Tension that wants resolution. Both contain the leading tone, which strongly pulls toward the tonic.
Predominant → Dominant → Tonic is one of the central motions in tonal music. In C major, Dm → G → C is ii → V → I. We will expand that sound when we add seventh chords in Module 3.
Choose a major key below. The chord names change, but the Roman-numeral pattern and chord qualities stay exactly the same.
C major: C · Dm · Em · F · G · Am · B°
The spelling changes with the key signature, but the quality order remains: Major, minor, minor, Major, Major, minor, diminished.
In G major, which chord should be the vi chord? The sixth scale degree is E, and vi is always minor in a major key.
Answer: Em. The full G-major set is G, Am, Bm, C, D, Em, F♯°.
A chord progression is simply a sequence of chords. Roman numerals let us recognize the same progression in any key.
C–F–G–C
Home → away → tension → home.
Dm–G–C
Predominant → dominant → tonic.
C–Am–Dm–G
A strong circular motion that leads naturally back to I.
C–G–Am–F
The same four functions can support countless melodies.
Play all seven C-major triads in order: C, Dm, Em, F, G, Am, B°. Then play Dm–G–C. Listen for the increasing sense of direction as ii moves to V, and the release when V resolves to I.
You can build the seven triads in any major key, identify them with Roman numerals, and understand their basic harmonic jobs. The next step is to add one more note to each chord.
Whole and half steps, scale degrees, triad construction, and chord qualities.
I, ii, iii, IV, V, vi, vii° and their basic functions.
Add the seventh and hear tension and resolution become even clearer.
See why roots moving by fourths feel inevitable.
Temporarily make any chord sound like home.
Compare jazz, pop, and classical harmonic choices.