Chords and progressions

A chord is three notes agreeing. A progression is them agreeing in a particular order, which is harder.

— the Slopwright

Stack every other note of a scale and you get a triad: a root, a third and a fifth. Built on each step of the major scale, the triads come out major, minor, minor, major, major, minor and diminished. Musicians number them with Roman numerals: I, ii, iii, IV, V, vi, vii°, capitals for major.

A progression is a sequence of chords. I feels like home, V wants to go home, IV moves away gently and vi is home on a cloudy day. Four of them, I V vi IV, carry a remarkable number of songs, and changing which one you start on changes the whole feel.

Add the next note up the stack and you get a seventh chord (maj7, m7, 7): softer, jazzier, or, for the plain 7, pulling hard towards the next chord.

Try this

1. In G major, play I, V, vi, IV with the chord buttons. Then play vi, IV, I, V: the same four, starting sad.
2. Play V then I, and V then vi. The second one is a deceptive cadence: the ear expects home and gets the cloudy version.
3. Turn on Sevenths and play the same progression again.