Why C major is C, E and G: what a triad really is

Melody is one note at a time. Chords are notes together, and they are the other half of music. If you have ever wondered why a song "sounds full" the moment a pianist puts their left hand down, this is why.

A chord is notes played together

That is the whole definition. Two notes at once is technically an interval; three or more notes at once is a chord. The most common kind of chord, and the one every other chord is built from, is the triad: three notes.

A triad is built by stacking thirds

Start on any note. That note is the root; it gives the chord its name. Now go up the scale from the root: play one, skip one, play one, skip one, play one. In C major that gives you:

• C, the root
• skip D, play E, the third
• skip F, play G, the fifth

C, E and G together are the C major triad. Every triad works the same way: play one, skip one, play one, skip one, play one. The distance from the root to the next chord note is called a third, which is why we say a triad is "stacked in thirds".

The middle note carries the mood

Keep C and G where they are and lower the E by one key, to E♭. You have just turned C major into C minor: C, E♭, G. Same root, same top, one note moved, and the whole mood flips from bright to dark.

That middle note, the third, is the one to listen for. Major has a major third above the root (four keys up, counting black keys). Minor has a minor third (three keys up). Once you can hear that difference, you can tell major from minor in any chord, in any song.

Try it on the keyboard

Find C: it is the white key just to the left of the pair of two black keys. Press C, then E, then G, one at a time, and then all three together. That sound is your first chord. Now lower the E to the black key just below it and play the three again. That is your second.

You can hear and play both right here: C major and C minor. The piano chord list has every major, minor and seventh chord on all twelve roots.

In PlayTheory this is step seven of Intro to Chords: the lesson waits until you have played the triad yourself, because a chord you have built with your own hands is a chord you will recognise for the rest of your life.