What a chord is built from

Play A major and then A minor: exactly one finger moves, and the effect shifts from bright to dark. All of harmony hangs on that one finger.

A chord isn't a shape to memorize but a stack built to a fixed pattern: a root, a note a third above it, and another third above that. Three stacked notes make a triad — steps 1, 3, and 5 of the corresponding scale. The root gives the chord its name; the fingering only determines where those three notes land on the strings. What looks like six notes on a guitar is the same three, doubled several times.

Of the three, the middle one carries the mood. Move the third down one fret and major becomes minor; root and top note stay untouched. That was the change at the start of this section — a chord's character rests on a single note.

Why thirds and not neighboring notes? Because a third is far enough apart not to rub and close enough to blend. Direct neighbors would produce a dense, unclear sound. This closes the circle back to melody: a chord is made of the same intervals as a melody, stacked instead of sequential. Add a fourth third on top and you get a four-note chord — the basis for the extensions in the next section.