// what is a chord?
A chord is three or more notes played at the same time. Where melody is horizontal — notes one after another — harmony is vertical. Notes stacked on top of each other.
The most basic chord is a triad — three notes built by stacking every other note of a scale. Take C, skip D, take E, skip F, take G. That's a C major triad — C E G.
Major vs minor: Major chords sound bright and happy. Minor chords sound darker and more emotional. The difference is just one note — the middle note of the triad moves down by one half step to make it minor. C major = C E G. C minor = C E♭ G.
// chord progressions
A chord progression is a sequence of chords that repeats through a song. Most songs use the same 3–4 chords over and over. The chords are numbered using Roman numerals based on their position in the scale.
The most common progression in all of popular music is I – V – vi – IV. In C major that's C – G – Am – F. Thousands of hit songs use exactly this progression.
I = C major (C E G)
V = G major (G B D)
vi = A minor (A C E)
IV = F major (F A C)
// why harmony works
Certain notes vibrate in simple mathematical ratios with each other — 2:1, 3:2, 4:3. These ratios sound pleasing to the human ear. That's why a C major chord sounds resolved and stable, while a diminished chord sounds tense and unstable.
Harmony is about tension and release. You move away from the home chord to create tension, then return to release it. That journey is what gives music its emotional arc.
On your piano app, play these four chords slowly in order — C+E+G, then G+B+D, then A+C+E, then F+A+C. Repeat. You just played the I–V–vi–IV progression. Recognise it? You've heard it in hundreds of songs. Now you know why it works.